Exhaust emission control device for internal combustion engine

ABSTRACT

Provided is an exhaust emission control device for an internal combustion engine capable of high-efficiency DPF regeneration processing. The exhaust emission control device comprises a DPF for collecting PMs in exhaust emissions, which is provided in an exhaust pipe of an engine, a fuel reformer for reforming fuel to manufacture a reducing gas containing hydrogen and carbon monoxide and supplying the reducing gas from an introduction port provided on the upstream side of the DPF of the exhaust pipe into the exhaust pipe, which is provided separately from the exhaust pipe, a catalyst converter for continuously oxidizing the reducing gas, which is provided between the introduction port and the DPF of the exhaust pipe, and a regeneration means for performing regeneration processing for burning the PMs collected by the DPF while the reducing gas is supplied into the exhaust pipe by the fuel reformer.

TECHNICAL FIELD

The present invention relates to an exhaust emission control device foran internal combustion engine. Specifically, it relates to an exhaustemission control device for an internal combustion engine having a DPF(diesel particulate filter) that collects PM (particulate matter) in theexhaust.

In addition, in the present invention, the terminology “rich” indicatesa ratio of air/fuel (hereinafter referred to as “air/fuel ratio”) offuel that is smaller than a stoichiometric air/fuel ratio, and theterminology “lean” indicates an air/fuel ratio of fuel that is largerthan the above stoichiometric air/fuel ratio. Moreover, in the followingexplanation, a mass ratio of air and fuel in a mixed gas flowing intothe engine is called an engine air/fuel ratio, and a mass ratio of airand combustible gas inside exhaust plumbing is called an exhaustair/fuel ratio.

In addition, as a method for controlling the exhaust air/fuel ratio,there is a method in which the exhaust air/fuel ratio is made low(hereinafter referred to as “enriching”) by reducing the intake airamount of the engine and adjusting the fuel injection (hereinafterreferred to as “main injection”) amount contributing to torque, and amethod in which the exhaust air/fuel ratio is enriched by performingfuel injection that does not contribute to torque (hereinafter referredto as “post injection”) to flow unburned fuel into the exhaust path.Moreover, alternatively, a method has also been known in which fuel isdirectly injected into the exhaust path (hereinafter referred to as“exhaust injection”).

BACKGROUND ART

Diesel engines, lean-burn engines, and the like have air/fuel ratiosinside the cylinders that become heterogeneous, and thus PM with carbonas a main component is emitted due to combusting in a state in whichoxygen is insufficient at a portion that has become locally rich.Consequently, in order to reduce the emission amount of such PM, atechnique has been widely used that reduces the emission amount of PM byproviding a DPF that collects PM in the exhaust to the exhaust system.Since there is a limitation to the PM amount that can be collected bythis DPF, a DPF regeneration process in which the PM deposited on theDPF is caused to combust is executed as appropriate. In recent years,various proposals have been made related to techniques for this DPFregeneration process.

For example, in Patent Document 1, an exhaust emission control device isexemplified that arranges a catalytic converter coated with a catalysthaving high oxidation performance in an exhaust channel on an upstreamside of the DPF, and that performs exhaust injection of unburned fuelinto the exhaust channel, thereby causing this fuel to combust in thecatalytic converter to raise the temperature of the exhaust, andcombusts PM deposited on the DPF by causing the exhaust thereby madehigh temperature to flow into the DPF.

In addition, in Patent Document 2, for example, an exhaust emissioncontrol device is exemplified that, by performing post injection insteadof exhaust injection as described above, causes fuel to be combusted inthe catalytic converter to raise the temperature of exhaust, similarlyto the exhaust emission control device of Patent Document 1, andcombusts PM deposited on the DPF.

Incidentally, in addition to this exhaust injection and post injection,a method has been known as a method to make the exhaust air/fuel ratiorich in which a fuel reformer that produces reducing gas containingcarbon monoxide and hydrogen by way of a reforming reaction is providedto the exhaust channel. Herein, as the reforming reaction of a reformingcatalyst of the fuel reformer, for example, a reaction has been knownthat produces a gas containing hydrogen and carbon monoxide by thepartial oxidation reaction of hydrocarbons, such as that shown informula (1) below.

C_(n)H_(m)+1/2nO₂ →nCO+1/2mH₂  (1)

This partial oxidation reaction is an exothermal reaction employing fueland oxygen, and the reaction progresses spontaneously. As a result, uponthe reaction being started, it is possible to continuously producehydrogen without the supply of heat from outside. In addition, in thiskind of partial oxidation reaction, in a case in which fuel and oxygencoexist in a high temperature state, the combustion reaction as shown informula (2) below also progresses on the reforming catalyst.

C_(n)H_(m)+(n+1/4m)O₂ →nCO₂+1/2mH₂ O  (2)

As the reforming reaction, in addition to the partial oxidationreaction, the steam reforming reaction as shown in formula (3) below hasalso been known.

C_(n) H _(m) +nH₂O→nCO+(n+1/2m)H₂  (3)

This steam reforming reaction is an endothermic reaction employing fueland steam, and is not a reaction that progresses spontaneously. As aresult, the steam reforming reaction is easily controlled relative tothe partial oxidation reaction described above. On the other hand, it isnecessary to input energy such as of a heat supply from outside.

Patent Document 1: Japanese Patent No. 3835241

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. H8-42326

Incidentally, if the oxygen amount flowing into the DPF suddenlyincreases while PM is being combusted by causing exhaust of a hightemperature to flow into the DPF, an oxidation reaction in the DPF maysuddenly progress and the DPF may melt. Herein, as main causes for asudden increase in the oxygen amount in the exhaust, for example, a casein which fuel injection has been interrupted (hereinafter referred to as“deceleration fuel-cut”) accompanying deceleration of the vehicle, acase in which the engine transitions to idle operation, or the like canbe exemplified.

In order to avoid such a situation, for example, it has been consideredto consume a surge in oxygen in the catalytic converter providedupstream of the DPF by way of performing exhaust injection or postinjection, as with the exhaust emission control devices exemplified inthe aforementioned Patent Documents 1 and 2, thereby lowering the oxygenamount flowing into the DPF.

However, in a case of performing exhaust injection as in the exhaustemission control device of Patent Document 1, unburned fuel makes directcontact with the catalytic converter, the temperature of the catalystsurface becomes high locally, and thus the catalyst may deteriorate dueto sintering or the like. In addition, when fuel contacts the catalystin a droplet state, the temperature of the catalyst surface at thecontacting portion thereof will decrease locally due to the latent heatof vaporization, and thus coking may occur. Moreover, if exhaustinjection is performed in a case in which the exhaust temperature islow, the exhaust temperature will decrease further due to the latentheat of vaporization of the fuel supplied by exhaust injection, wherebyliquid fuel collects in the exhaust channel, the catalyst deteriorates,and exhaust system components may corrode.

In addition, in a case of performing post injection as in the exhaustemission control device of Patent Document 2, a portion of the fuelinjected adheres to the surface of the wall of the cylinders, and thusthis fuel may mix into the engine oil. In such a case, not only the fuelinjected not contributing to combustion of PM, but also so-called oildilution in which engine oil is diluted by this fuel may occur.

Moreover, a majority of the reducing agent consumed by the oxidationreaction in the catalytic converter, as in the exhaust emission controldevice of Patent Documents 1 and 2, is hydrocarbons. Therefore, it isnecessary to maintain the catalytic converter at a certain temperatureat which the oxidation reaction of the hydrocarbons flowing thereinto ispossible. However, in a case in which low-load operation continues orthe like, the temperature of the catalytic converter will decrease to atemperature at which it is difficult for the oxidation reaction tooccur, and the DPF regeneration process may not be able to be executed.

On the other hand, in a case of providing a fuel reformer in an exhaustchannel, there are the following issues.

Specifically, in a case of providing the fuel reformer in an exhaustchannel having an exhaust amount that regularly fluctuates as describedabove, it is necessary to increase the reaction time for which thereforming catalyst of the fuel reformer and the exhaust come intocontact, in order to effectively produce hydrogen in this fuel reformer.However, in order to increase the reaction time as such, it is necessaryto increase the size of the reforming catalyst, which may raise cost.

In addition, in order to operate the fuel reformer in a stable state, itis necessary to maintain the reaction temperature of the reformingcatalyst of this fuel reformer to be constant. However, when providing afuel reformer in an exhaust channel for which the oxygen amount, steamamount, and temperature are always fluctuating as described above, itbecomes difficult to operate the fuel reformer in a stable state.

Incidentally, in addition to the aforementioned DPF, a technique hasbeen known from the prior art in which NOx (nitrogen oxides) in exhaustis absorbed by providing a NOx purification catalyst in the exhaustsystem of the internal combustion engine, thereby reducing the emittedamount of NOx. On the other hand, sulfur components in the fuel andengine oil are contained in exhaust emitted from the internal combustionengine. When such sulfur components accumulate on the NOx purificationcatalyst, the NOx purification performance declines. Therefore, thefollowing technique has been proposed that aims to prevent thepurification performance from declining due to such poisoning of the NOxpurification catalyst.

For example, an exhaust emission control device that provides a fuelreformer, which produces a reducing gas containing hydrogen, carbonmonoxide, etc. by way of a reforming reaction, upstream of a NOxpurification catalyst is proposed in Patent Document 3. According tothis exhaust emission control device, removal of sulfur components ispromoted by adding hydrogen thus produced by the fuel reformer to theexhaust when executing the SOx regeneration process of the NOxpurification catalyst.

Such a SOx regeneration process of a NOx purification catalyst and a DPFregeneration process of the aforementioned DPF are basically executedseparately according to the states of the NOx purification catalyst andthe DPF. However, even in a case of performing either of theregeneration processes, it is necessary to cause the temperature of theexhaust system to rise. Therefore, in order to prevent the fuel economyfrom deteriorating, it is more preferable to execute the SOxregeneration process and the DPF regeneration process simultaneouslythan to execute individually.

Consequently, in Patent Document 4, for example, an exhaust emissioncontrol device has been proposed in which the NOx purification catalystis provided downstream of the DPF, and the DPF regeneration process ofthe DPF and the SOx regeneration process of the NOx purificationcatalyst are executed simultaneously by controlling the oxygenconcentration flowing into the DPF.

Patent Document 3: Japanese Patent No. 3896923

Patent Document 4: Japanese Unexamined Patent Application PublicationNo. 2005-133721

Incidentally, in a case of executing the SOx regeneration process of theNOx purification catalyst, it is necessary to make the exhaust air/fuelratio flowing into this NOx purification catalyst to be less than astoichiometric ratio. On the other hand, in a case of executing the DPFregeneration process of the DPF, it is necessary to make the exhaustair/fuel ratio flowing into the DPF to be larger than the stoichiometricratio, thereby making an oxygen-excess atmosphere.

The exhaust emission control device illustrated in the aforementionedPatent Document 4 aims to adjust the oxygen concentration of the exhaustflowing into the NOx purification catalyst by controlling the oxygenconcentration of exhaust flowing into the DPF, and to execute the DPFregeneration process and SOx regeneration process simultaneously.However, with the exhaust emission control device of Patent Document 4,when the oxygen concentration of exhaust flowing into the DPF becomeshigh, the exhaust air/fuel ratio flowing into the NOx purificationcatalyst will become large, and thus it is difficult to simultaneouslyexecute the DPF regeneration process and the SOx regeneration processwith high efficiency. As a result, the time consumed in thissimultaneous process will become long, whereby fuel economy maydeteriorate and the catalyst may degrade.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As described above, with the exhaust emission control devicesillustrated in Patent Documents 1 and 2 and the exhaust emission controldevices provided with a fuel reformer in the exhaust channel, theefficiency of the DPF regeneration process may decline depending on theoperating state of the internal combustion engine.

In addition, with the exhaust emission control device illustrated inPatent Document 4, in a case of performing the DPF regeneration processand the SOx regeneration process simultaneously, the efficiency of theprocesses may decline.

An object of the present invention is to provide an exhaust emissioncontrol device for an internal combustion engine that can perform a DPFregeneration process with high efficiency irrespective of the operatingstate of the internal combustion engine. In addition, concomitant withthis, providing an exhaust emission control device for an internalcombustion engine that can simultaneously execute a DPF regenerationprocess and SOx regeneration process with high efficiency is also madean object of the present invention.

Means for Solving the Problems

In order to achieve the above objects, the present invention provides anexhaust emission control device for an internal combustion engine (1)including a particulate filter (32) that is provided in an exhaustchannel (4, 5) of the internal combustion engine, and collectsparticulates in exhaust. The exhaust emission control device includes afuel reformer (50) that is provided separately from the exhaust channel,produces a reducing gas containing hydrogen and carbon monoxide byreforming fuel, and supplies the reducing gas from an inlet (14)provided in the exhaust channel upstream of the particulate filter intothe exhaust channel; a catalytic converter (31) that is provided in theexhaust channel between the inlet and the particulate filter, andcontinuously oxidizes the reducing gas; and a regeneration means (40)for executing a regeneration process to cause particulates collected inthe particulate filter to be combusted while supplying reducing gas fromthe fuel reformer into the exhaust channel.

According to this configuration, the catalytic converter thatcontinuously oxidizes reducing gas is provided in the exhaust channelbetween the particulate filter and the inlet at which reducing gasproduced by the fuel reformer is supplied, and furthermore, theregeneration means that executes the regeneration process causingparticulates to combust while supplying reducing gas into the exhaustchannel is provided therein.

This enables the oxygen concentration of exhaust flowing into theparticulate filter to be controlled irrespective of the operating stateof the internal combustion engine, by supplying reducing gas into theexhaust channel when executing the regeneration process. As a result,even in a case in which the particulate filter may melt such as duringan idle operating state or fuel-cut state described above, this can beavoided by lowering the oxygen concentration. This enables theregeneration process to be stably executed irrespective of the operatingstate of the internal combustion engine.

In addition, by employing such a reducing gas, the temperature of theexhaust can be raised without supplying unburned fuel such as in exhaustinjection and post injection. This enables problems such as theoccurrence of coking, degradation and corrosion of the catalyst andcomponents of the exhaust channel, deterioration in fuel economy, andoccurrence of oil dilution as described above to be avoided.

In addition, the molecular diameters of carbon monoxide and hydrogencontained in the reducing gas are small compared to the moleculardiameters of the hydrocarbons supplied by exhaust injection and postinjection. As a result, even in a case of a great amount of particulatesdepositing on the particulate filter, it is possible to supply reducinggas along with oxygen to deep parts thereof. This can effectivelypromote the combustion of particulates.

In addition, by providing the fuel reformer that supplies reducing gasto be separate from the exhaust channel, the regeneration time period ofthe particulate filter can be decided independently of the state of theinternal combustion engine. Therefore, the regeneration process of theparticulate filter can be suitable executed as needed while alwayscontrolling the internal combustion engine to an optimal state.Moreover, by providing the fuel reformer to be separate from the exhaustchannel, reducing gas can always be produced at optimum efficiency andthis reducing gas can be supplied into the exhaust channel, irrespectiveof the operating state of the internal combustion engine, oxygenconcentration and steam concentration of exhaust, etc.

On the other hand, in a case of providing the fuel reformer inside theexhaust channel, it is necessary to enlarge the fuel reformer so as tobe able to operate without influencing the components, temperature, andflow rate of the exhaust; however, according to this configuration, itis possible to perform operation stably without enlarging the device byproviding the fuel reformer to be separate from the exhaust channel. Inaddition, by providing the fuel reformer to be separate from the exhaustchannel, it becomes possible to activate the catalyst provided to thefuel reformer at an early stage, by performing control of an independentsystem from the control of the internal combustion engine.

In order to achieve the above-mentioned object, the present inventionprovides an exhaust emission control device for an internal combustionengine (1) including a particulate filter that is provided in an exhaustchannel (4, 5) of the internal combustion engine, and collectsparticulates in exhaust. The exhaust emission control device includes afuel reformer (50) that is provided separately from the exhaust channel,produces a reducing gas containing hydrogen and carbon monoxide byreforming fuel, and supplies the reducing gas from an inlet (14)provided in the exhaust channel upstream of the particulate filter intothe exhaust channel; and a regeneration means (40) for executing aregeneration process to cause particulates collected in the particulatefilter to be combusted while supplying reducing gas from the fuelreformer into the exhaust channel. A catalyst having an oxidativefunction of continuously oxidizing reducing gas is supported on theparticulate filter.

According to this configuration, in addition to effects similar to theabove-mentioned exhaust emission control device, by supporting acatalyst having an oxidative function on the particulate filter, theexhaust emission control device can be made compact, and the combustionreaction of particulates can be further promoted. Therefore, the timefrom supplying reducing gas until combustion of particulates begins canbe further shortened.

Preferably, the catalytic converter contains at least one selected fromthe group consisting of platinum, palladium, and rhodium.

According to this configuration, the catalytic converter contains atleast one selected from the group consisting of platinum, palladium, andrhodium. By containing these active species, the catalytic combustionreaction such as of hydrogen, carbon monoxide, and light hydrocarbonscontained in the reducing gas can be promoted.

Preferably, the catalyst having the oxidative function contains at leastone selected from the group consisting of palladium, rhodium, platinum,silver, and gold.

According to this configuration, the catalyst supported on theparticulate filter contains at least one selected from the groupconsisting of palladium, rhodium, platinum, silver, and gold. Thisenables effects similar to the above-mentioned exhaust emission controldevice to be exerted.

Preferably, the exhaust emission control device further includes anoxygen concentration detection means (23) for detecting or estimating anoxygen concentration (AF) of exhaust in the exhaust channel flowing intothe particulate filter.

According to this configuration, an oxygen concentration detection meansis provided for detecting the oxygen concentration of exhaust flowinginto the particulate filter. This enables the oxygen concentration ofexhaust flowing into the particulate filter to be controlled to apredetermined target value with good accuracy. Moreover, by controllingthe oxygen concentration of exhaust flowing into the particulate filter,an excessive rise in temperature of the particulate filter duringexecution of the regeneration process can be prevented.

Preferably, the reducing gas produced by the fuel reformer contains morecarbon monoxide than hydrogen.

According to this configuration, more carbon monoxide than hydrogen iscontained in the reducing gas. Carbon monoxide combusts at a lowertemperature than hydrogen. Particulates deposited on the particulatefilter can be effectively combusted by supplying such a reducing gascontaining carbon monoxide.

Preferably, a temperature of the reducing gas supplied by the fuelreformer is higher than a temperature of exhaust flowing through theexhaust channel at the inlet.

According to this configuration, reducing gas is supplied at atemperature higher than the temperature of exhaust flowing through theexhaust channel at the inlet. This enables the combustion ofparticulates to be promoted by causing the temperature of the exhaustflowing into the catalytic converter to rise.

Preferably, the exhaust emission control device further includes atarget concentration setting means (40) for setting an oxygenconcentration target value (AFTV) of exhaust flowing into theparticulate filter while executing the regeneration process by way ofthe regeneration means; and an oxygen concentration control means (40)for controlling the oxygen concentration (AF) of exhaust so as to matchthe oxygen concentration target value (AFTV) thus set by the oxygenconcentration setting means, by adjusting at least one amount an intakeair amount of the internal combustion engine, an exhaust recirculationratio of the internal combustion engine, a fuel injection amount of theinternal combustion engine, and a supply amount of reducing gas from thefuel reformer.

According to this configuration, while executing the regenerationprocess, the oxygen concentration of exhaust flowing into theparticulate filter is controlled so as to match the target oxygenconcentration by adjusting at least one among the intake air amount,exhaust recirculation ratio, fuel injection amount, and supply amount ofreducing gas. This enables the oxygen concentration of exhaust to bemade to match the target oxygen concentration with good accuracy.

Preferably, the target concentration setting means sets the oxygenconcentration target value (AFTV) based on at least one among a flowrate (GE) of exhaust flowing through the exhaust channel, a temperature(TE) of the exhaust, and a deposition amount (QPM) of particulatesdeposited on the particulate filter.

According to this configuration, the oxygen concentration target valueis set based on at least one among the flow rate of exhaust flowingthrough the exhaust channel, the temperature of exhaust, and thedeposition amount of particulates deposited on the particulate filter.This enables the target oxygen concentration to be set so thatparticulates are made to combust at an adequate temperature.

Preferably, the target concentration setting means, in a case of theinternal combustion engine being in an idle operating state, sets theoxygen concentration target value to be low compared to a case of notbeing in an idle operating state.

According to this configuration, in a case of the internal combustionengine being in an idle operating state, the oxygen concentration targetvalue is set to be low compared to a case of not being in an idleoperating state. With this, even in a case in which the oxygenconcentration in exhaust increases with the internal combustion enginehaving transitioned to an idle operating state, the oxidation reactionin the particulate filter is suppressed by setting the oxygenconcentration target value to be low, and thus an excessive rise intemperature of this particulate filter can be prevented.

Preferably, the target concentration setting means, in a case of theinternal combustion engine being in a deceleration operating state, setsthe oxygen concentration target value to be low compared to a case ofnot being in a deceleration operating state.

According to this configuration, in a case of the internal combustionengine being in a deceleration operating state, the oxygen concentrationtarget value is set to be low compared to a case of not being in adeceleration operating state. With this, even in a case in which theoxygen concentration in exhaust increases with the internal combustionengine transitioning to a deceleration operating state and decelerationfuel-cut having been performed, the oxidation reaction in theparticulate filter is suppressed by setting the oxygen concentrationtarget value to be low, and thus an excessive rise in temperature ofthis particulate filter can be prevented.

Preferably, the fuel reformer produces reducing gas with carbon monoxideas a main component by way of a partial oxidation reaction ofhydrocarbon fuel and air.

According to this configuration, this fuel reformer can be made asmaller size by producing the reducing gas by way of the partialoxidation reaction. In order words, this is because a device tocontinually supply extra energy from outside does not need to beprovided since the partial oxidation reaction as described above is anexothermic reaction, and once the reaction starts, the reactionprogresses spontaneously. In addition, there is also no need to alsoprovide a converter and system for concentrating hydrogen of a shiftreaction, etc. Moreover, the light-off time of the fuel reformer can beshortened by making the fuel reformer to be small in this way.Therefore, reducing gas can be quickly supplied into the exhaust channelas needed.

Furthermore, by introducing light hydrocarbons generated secondarily inthis partial oxidation reaction to the catalytic converter along withcarbon monoxide and hydrogen, it can also be used in raising thetemperature of exhaust.

In order to achieve the above objects, the present invention provides anexhaust emission control device for an internal combustion engine (1)including a particulate filter (32) that is provided in an exhaustchannel (4) of the internal combustion engine, and collects particulatesin exhaust. The exhaust emission control device includes a regenerationmeans (40A) for executing a regeneration process to cause particulatescollected in the particulate filter to be combusted; and a fuel reformer(50) that is provided separately from the exhaust channel, produces areducing gas containing hydrogen and carbon monoxide by reforming fuel,and supplies the reducing gas from an inlet (14) provided in the exhaustchannel upstream of the particulate filter into the exhaust channel. Theregeneration means includes a normal regeneration means (40A) thatexecutes a regeneration process without employing reducing gas producedby the fuel reformer, and a heated regeneration means (40A) that allowsa regeneration process employing reducing gas produced by the fuelreformer to be executed, and switches between executing the regenerationprocess by way of the normal regeneration means and executing theregeneration process by way of the heated regeneration means accordingto a predetermined condition.

According to this configuration, when executing the regeneration processin which particulates collected in the particulate filter are caused tocombust, the normal regeneration means that executes the regenerationprocess without employing reducing gas and the heated regeneration meansthat allows execution of the regeneration process employing reducing gasare switched according to predetermined conditions. Herein, moleculesthat easily combust such as hydrogen and carbon monoxide are containedin the reducing gas produced by the fuel reformer. Even in a state inwhich the exhaust temperature is low and it is difficult to causeparticulates to combust, the temperature of exhaust can be quicklyraised by supplying such a reducing gas to the particulate filter, forexample. In addition, by switching between the normal regeneration meansand heated regeneration means according to predetermined conditions, forexample, a regeneration process can be executed even if it enters astate in which a regeneration process on the particulate filter would bedifficult to execute by a conventional method as described above, suchas in a case of immediately after engine startup or having transitionedto low-load operation. In other words, it is possible to reduce thefrequency at which the operating state of the internal combustion engineenters a situation in which it is difficult to continue the regenerationprocess on the particulate filter, thereby forcing interruption of theregeneration process. Therefore, the time required in the regenerationprocess can be shortened.

In addition, by employing such a reducing gas, the temperature ofexhaust can be made to rise without supplying unburned fuel as inexhaust injection and post injection. This enables problems such as theoccurrence of coking, degradation and corrosion of the catalyst andcomponents of the exhaust channel, deterioration in fuel economy, andoccurrence of oil dilution as described above to be avoided.

In addition, the molecular diameters of carbon monoxide and hydrogencontained in the reducing gas are small compared to the moleculardiameters of the hydrocarbons supplied by exhaust injection and postinjection. As a result, even in a case of a great amount of particulatesdepositing on the particulate filter, it is possible to supply reducinggas along with oxygen to deep parts thereof. This can effectivelypromote the combustion of particulates.

In addition, by providing the fuel reformer that supplies reducing gasto be separate from the exhaust channel, the regeneration time period ofparticulates can be decided independently of the state of the internalcombustion engine. Therefore, the regeneration process on theparticulate filter can be suitable executed as needed while alwayscontrolling the internal combustion engine to an optimal state. Inaddition, by providing the fuel reformer to be separate from the exhaustchannel, reducing gas can always be produced at optimum efficiency andthis reducing gas can be supplied into the exhaust channel, irrespectiveof the operating state of the internal combustion engine, oxygenconcentration and steam concentration of exhaust, etc.

On the other hand, in a case of providing the fuel reformer inside theexhaust channel, it is necessary to enlarge the fuel reformer so as tobe able to operate without influencing the components, temperature, andflow rate of the exhaust; however, according to this configuration, itis possible to perform operation stably without enlarging the device byproviding the fuel reformer to be separate from the exhaust channel. Inaddition, by providing the fuel reformer to be separate from the exhaustchannel, it becomes possible to activate the catalyst provided to thefuel reformer at an early stage, by performing control of an independentsystem from the control of the internal combustion engine.

Preferably, the reducing gas produced by the fuel reformer contains morecarbon monoxide than hydrogen.

According to this configuration, more carbon monoxide than hydrogen iscontained in the reducing gas. Carbon monoxide combusts at a lowertemperature than hydrogen. Particulates deposited on the particulatefilter can be efficiently combusted by supplying such a reducing gascontaining carbon monoxide.

Preferably, the catalytic converter (31) that continuously oxidizesreducing gas is provided in the exhaust channel between the inlet andthe particulate filter.

According to this configuration, the reducing gas produced by the fuelreformer flows into the catalytic converter and combusts by way of thiscatalytic converter. By combusting reducing gas by way of the catalyticconverter in this way, the temperature of exhaust is raised, andparticulates deposited on the particulate filter can be efficientlycombusted.

Preferably, the exhaust emission control device further includes acombustion judgment means (40A, 29D) for judging whether particulatesdeposited on the particulate filter are in a combusted state. Theregeneration means executes the regeneration process by way of thenormal regeneration means in a case of having been judged that theparticulate are in a combusted state, and executes the regenerationprocess by way of the heated regeneration means in a case of having beenjudged that the particulates are not in a combusted state.

According to this configuration, in a case of having determined that theparticulates deposited on the particulate filter are in a combustedstate, a regeneration process not employing reducing gas is executed byway of the normal regeneration means, and in a case of having determinedthat the particulates are not in a combusted state, a regenerationprocess is executing employing reducing gas by way of the heatedregeneration means. This enables the regeneration process to beefficiently executed while preventing the reducing gas from beingconsumed for no purpose.

Preferably, the exhaust emission control device further includes anoxygen concentration detection means for detecting or estimating anoxygen concentration of exhaust in the exhaust channel on a downstreamside of the particulate filter. The combustion judgment means judgeswhether the particulates are in a combusted state based on the oxygenconcentration thus detected or estimated by the oxygen concentrationdetection means.

According to this configuration, it is determined whether theparticulates are in a combusted state based on the oxygen concentrationon a downstream side of the particulate filter. This enables thecombusted state of particulates to be determined with good accuracy.

Preferably, the exhaust emission control device further includes adownstream exhaust temperature detection means (29D) for detecting orestimating an exhaust temperature (TD) in the exhaust channel on adownstream side of the particulate filter. The combustion judgment meansjudges whether the particulates are in a combusted state based on theexhaust temperature (TD) thus detected or estimated by the downstreamexhaust temperature detection means.

According to this configuration, it is determined whether theparticulates are in a combusted state based on the exhaust temperatureon a downstream side of the particulate filter. This enables thecombusted state of particulates to be determined with good accuracy.

Preferably, the heated regeneration means reduces the intake air amount(GE) of the internal combustion engine, increases the exhaustrecirculation ratio of the internal combustion engine, or sets thecharge efficiency of the internal combustion engine to be small,compared to a case of performing the regeneration process by way of thenormal regeneration means.

According to this configuration, in a case of executing the regenerationprocess by way of the heated regeneration means, the intake air amountof the internal combustion engine is reduced, the exhaust recirculationratio of the internal combustion engine is increased, or the chargeefficiency of the internal combustion engine is set to be small,compared to a case of executing the regeneration process by way of thenormal regeneration means. By executing the regeneration process by wayof such a heated regeneration means, the temperature of the particulatefilter can be quickly raised.

Preferably, the heated regeneration means includes a first heatedregeneration means (40A) for executing a regeneration process whilesupplying reducing gas from the fuel reformer into the exhaust channel,and a second heated regeneration means (40A) for executing aregeneration process without supplying reducing gas from the fuelreformer into the exhaust channel, and switches between executing theregeneration process by way of the first heated regeneration means andexecuting the regeneration process by way of the second heatedregeneration means according to a predetermined condition.

According to this configuration, a first heated regeneration means forexecuting a regeneration process while supplying reducing gas and asecond heated regeneration means for executing a regeneration processwithout supplying reducing gas are provided to the heated regenerationmeans, and the first heated regeneration means and the secondregeneration means are switched according to predetermined conditions.This enables the regeneration process to be appropriately executedaccording to the conditions.

Preferably, the exhaust emission control device further includes anupstream exhaust temperature detection means (29U) for detecting orestimating a temperature (TU) of exhaust in the exhaust channel on anupstream side of the particulate filter. The heated regeneration meansexecutes the regeneration process by way of the first heatedregeneration means in a case of the temperature (TU) thus detected bythe upstream exhaust temperature detection means being lower than apredetermined judgment value (TCTH).

According to this configuration, in a case in which the exhausttemperature on an upstream side of the particulate filter is less thanthe predetermined judgment value, the regeneration process is executedby way of the first heated regeneration means while supplying reducinggas. With this, even in a state in which the exhaust temperature is lowand it is difficult to cause the particulates to combust, the exhausttemperature is quickly raised, and thus combustion of the particulatescan be promoted.

Preferably, the exhaust emission control device further includes afilter temperature estimation means for estimating or detecting atemperature (TDPF) of the particulate filter. The heated regenerationmeans executes the regeneration process by way of the first heatedregeneration means in a case of the temperature (TDPF) thus estimated ordetected by the filter temperature estimation means being lower than apredetermined judgment value (TDTH).

According to this configuration, in a case of the temperature of theparticulate filter being lower than the predetermined judgment value,the regeneration process is executed by way of the first heatedregeneration means while supplying reducing gas. With this, even in astate in which the temperature of the particulate filter is low and itis difficult to cause particulates to combust, the exhaust temperatureis quickly raised, and thus the combustion of the particulates can bepromoted.

Preferably, the exhaust emission control device further includes atorque estimation means (40A) for estimating a generated torque (TRQ) ofthe internal combustion engine. The heated regeneration means executesthe regeneration process by way of the first regeneration means in acase of the generated torque (TRQ) thus estimated or detected by thetorque estimation means being less than a predetermined judgment value(TRQTH).

According to this configuration, in a case of the generated torque beinglower than the predetermined judgment value, the regeneration process isexecuted by way of the first heated regeneration means while supplyingreducing gas. With this, even in a state in which the internalcombustion engine is in a low-load operating state and it is difficultto cause particulates to combust, the exhaust temperature is quicklyraised, and thus the combustion of the particulates can be promoted.

Preferably, the torque estimation means estimates the generated torqueof the internal combustion engine based on at least one among arevolution speed of the internal combustion engine, a fuel injectionamount, and a fuel injection timing.

Preferably, the exhaust emission control device further includes atiming means (40A) for measuring an elapsed time (TIM) since starting upthe internal combustion engine. The heated regeneration means executesthe regeneration process by way of the first heated regeneration meansin a case of the elapsed time (TIM) thus measured by the timing meansbeing less than a predetermined judgment value (TIMTH).

According to this configuration, in a case of the elapsed time fromstarting up the internal combustion engine is less than thepredetermined judgment value, the regeneration process is executed whilesupplying reducing gas. With this, even in a case of not being longafter startup of the internal combustion engine and it being difficultto cause particulates to combust, the exhaust temperature is quicklyraised, and thus the combustion of particulates can be promoted.

In order to achieve the above objects, the present invention provides anexhaust emission control device for an internal combustion engine (1),including a NOx purification catalyst (33) that is provided in anexhaust channel (4,5) of the internal combustion engine and that, withan air/fuel ratio of exhaust flowing through the exhaust channel as anexhaust air/fuel ratio, adsorbs or occludes NOx in exhaust when theexhaust air/fuel ratio is made lean, and reduces the NOx adsorbed oroccluded when the exhaust air fuel ratio is made rich, and a particulatefilter (32) that is provided in the exhaust channel further upstreamthan the NOx purification catalyst, and that collects particulates inexhaust. The exhaust emission control device includes a fuel reformer(50B) that is provided separately from the exhaust channel, produces areducing gas containing hydrogen and carbon monoxide by reforming fuel,and supplies the reducing gas from an inlet (14B) provided in theexhaust channel between the particulate filter and the NOx purificationcatalyst into the exhaust channel.

According to this configuration, the particulate filter is provided inthe exhaust channel on an upstream side of the NOx purificationcatalyst, and the fuel reformer is provided that supplies reducing gascontaining hydrogen and carbon monoxide from the inlet provided betweenthis NOx purification catalyst and this particulate filter. With this,the exhaust air/fuel ratio of exhaust flowing into the NOx purificationcatalyst is kept low and the SOx regeneration process of the NOxpurification catalyst can be executed with high efficiency by supplyingreducing gas from downstream of the particulate filter, while the oxygenconcentration of exhaust flowing into the particulate is kept high, andthe regeneration process on the particulate filter is executed with highefficiency. In this way, according to this configuration, it is possibleto execute the regeneration process on the particulate filter and theSOx regeneration process simultaneously with high efficiency. Therefore,the time required in these processes is shortened, which can improvefuel economy, whereby degradation to the particulate filter and the NOxpurification catalyst can also be reduced.

In addition, by providing the fuel reformer to be separate from theexhaust channel, reducing gas can be supplied without increasing theheat capacity upstream of the NOx purification catalyst. This enablesthe SOx regeneration process to be executed without reducing the NOxpurification performance when at low temperature such as immediatelyafter engine startup.

Moreover, by providing the fuel reformer that produces reducing gas tobe separate from the exhaust channel, the execution time period of theSOx regeneration process can be decided independently of the state ofthe internal combustion engine. Therefore, the SOx regeneration processcan be suitable executed as needed while always controlling the internalcombustion engine to an optimal state. In addition, by providing thefuel reformer to be separate from the exhaust channel, reducing gas canalways be produced at optimum efficiency and this reducing gas can besupplied into the exhaust channel, irrespective of the operating stateof the internal combustion engine, the oxygen concentration or steamconcentration of the exhaust, etc.

On the other hand, in a case of providing the fuel reformer inside theexhaust channel, it is necessary to enlarge the fuel reformer so as tobe able to operate without influencing the components, temperature, andflow rate of the exhaust; however, according to this configuration, itis possible to perform operation stably without enlarging the device byproviding the fuel reformer to be separate from the exhaust channel. Inaddition, by providing the fuel reformer to be separate from the exhaustchannel, it becomes possible to activate the catalyst provided to thefuel reformer at an early stage by performing control of an independentsystem from the control of the internal combustion engine.

Preferably, the reducing gas produced by the fuel reformer is at apressure higher than atmospheric pressure, and contains more carbonmonoxide than hydrogen by volume ratio.

According to this configuration, more carbon monoxide than hydrogen iscontained in the reducing gas by volume ratio. Moreover, the temperatureat which carbon monoxide begins to combust on the catalyst is atemperature lower than the temperature at which hydrogen begins tocombust. The NOx purification catalyst is quickly raised in temperatureby supplying such a reducing gas containing carbon monoxide, and thusthe purification of SOx can be promoted in the SOx regeneration process.In addition, reducing gas thus produced can be supplied into the exhaustchannel without adding an extra device by producing reducing gas of apressure higher than atmospheric.

Preferably, a temperature of the reducing gas supplied by the fuelreformer is higher than a temperature of exhaust flowing through theexhaust channel at the inlet.

According to this configuration, reducing gas of a temperature higherthan the temperature of exhaust flowing through the exhaust channel atthe inlet is supplied. This enables the NOx purification catalyst to bequickly raised in temperature, and thus the purification of SOx to bepromoted in the SOx regeneration process.

Preferably, oxygen is contained in the exhaust flowing through theexhaust channel when reducing gas from the fuel reformer is introducedinto the exhaust channel.

Preferably, the exhaust emission control device further includes: aregeneration means (40B) for selectively executing a normal regenerationoperation that raises the particulate filter in temperature to causeparticulates collected in the particulate filter to combust, and asimultaneous regeneration operation that supplies reducing gas from thefuel reformer into the exhaust channel while executing the normalregeneration operation to purify SOx adsorbed to the NOx purificationcatalyst according to a predetermined condition.

According to this configuration, the normal regeneration operation thatperforms the regeneration process on the particulate filter and thesimultaneous regeneration operation that supplies reducing gas andperforms the SOx regeneration process while executing this normalregeneration operation are selectively executed according topredetermined conditions. This enables these regeneration processes tobe efficiently executed while minimizing consumption of reducing gas, byexecuting the normal regeneration operation in a case of only performingthe regeneration process on the particulate filter being necessary, andexecuting the simultaneous operation process in a case in whichperforming the regeneration process on the particulate filter and theSOx regeneration process simultaneously is preferable.

Preferably, the exhaust emission control device further includes anexhaust temperature control means (40B) for controlling a temperature ofexhaust when executing the normal regeneration operation by adjusting atleast one among an intake air amount and boost pressure.

According to this configuration, the temperature of the exhaust iscontrolled by adjusting at least one among the intake air amount and theboost pressure when executing the normal regeneration operation. Thisenables the temperature of the exhaust to be controlled to a requiredtemperature in order for the particulates to be made to combust, and theregeneration process on the particulate filter to be performedefficiently.

Preferably, a catalytic converter (31) having an oxidative function isprovided in the exhaust channel on an upstream side of the particulatefilter. The regeneration means executes post injection when executingthe normal regeneration operation.

According to this configuration, when providing the catalytic converterhaving an oxidative function on an upstream side of the particulatefilter, post injection is executed while executing the normalregeneration operation. With this, the temperature of the exhaustflowing into the particulate filter can be raised and thus theregeneration process on the particulate filter can be performed withhigh efficiency, by causing fuel supplied by way of post injection tocombust by way of the catalytic converter.

Preferably, a catalyst having an oxidative function is supported on theparticulate filter. The regeneration means executes post injection whenexecuting the normal regeneration operation.

According to this configuration, when the catalyst having an oxidativefunction is made to be supported on the particulate filter, postinjection is executed while executing the normal regeneration operation.Therefore, by causing fuel supplied by post injection to combust by wayof the catalytic converter when executing the normal regenerationoperation, the temperature of the exhaust flowing into the particulatefilter is raised, and thus the regeneration process on the particulatefilter can be executed with high efficiency. In addition, the exhaustemission control device can be made compact, and the combustion reactionof particulates can be further promoted, compared to a case of providingthe catalytic converter and the particulate filter separately. Thisenables the efficiency of the regeneration process on the particulatefilter to be further improved.

Preferably, the exhaust emission control device further includes aparticulate deposition amount estimation means (40B, 27) for estimatingor detecting a particulate deposition amount (QPM) of the particulatefilter. The regeneration means executes the normal regenerationoperation or the simultaneous regeneration operation in response to theparticulate deposition amount (QPM) thus estimated or detected by theparticulate deposition amount estimation means having become at least apredetermined first estimation judgment value (QPMATH).

According to this configuration, in a case of the particulate depositionamount having become at least the first deposition judgment value, thenormal regeneration operation or the simultaneous regeneration operationis executed. This enables the regeneration process on the particulatefilter to be executed at a suitable opportunity prior to the depositionamount of particulates reaching the limit.

Preferably, the exhaust emission control device further includes acatalyst temperature estimation means (40B, 26B) for estimating ordetecting a temperature (TLNC) of the NOx purification catalyst; and aSOx poisoning amount estimation means (40B, 28) for estimating ordetecting a SOx poisoning amount (QSO) of the NOx purification catalyst.The regeneration means executes the simultaneous regeneration operationin response to the temperature (TLNC) thus estimated or detected by thecatalyst temperature estimation means being at least a predeterminedtemperature judgment value (TLNCTH), and the SOx poisoning amount (QSO)thus estimated or detected by the SOx poisoning amount estimation meanshaving become at least a predetermined first poisoning judgment value(QSOATH).

According to this configuration, the simultaneous regeneration operationis executed in response to the temperature of the NOx purificationcatalyst being at least the predetermined temperature judgment value andthe SOx poisoning amount of the NOx purification catalyst having becomeat least the first poisoning judgment value. This enables the SOxregeneration process to be performed at an opportunity before the NOxpurification performance of the NOx purification catalyst declinesdrastically. Furthermore, SOx desorbed from the NOx purificationcatalyst can be purified with good efficiency by executing thesimultaneous regeneration operation in a case in which the temperatureof the NOx purification catalyst is at least the predeterminedtemperature judgment value.

Preferably, the regeneration means ends execution of the simultaneousregeneration operation and executes the normal regeneration operation,in response to the SOx poisoning amount (QSO) estimated or detected bythe SOx poisoning amount estimation means having become smaller than apredetermined second poisoning judgment value (QSOBTH).

According to this configuration, execution of the simultaneousregeneration operation ends in response to the SOx poisoning amounthaving become less than the predetermined second poisoning judgmentvalue, and the normal regeneration operation is executed. This enablesexecution of the simultaneous regeneration operation to end according torecovery of the NOx purification performance of the NOx purificationcatalyst, and the regeneration process on the particulate filter tocontinue.

Preferably, the exhaust emission control device further includes anoxygen concentration detection means (23B) for detecting an oxygenconcentration of exhaust in the exhaust channel in a vicinity of the NOxpurification catalyst; and a supply amount control means (40B) forcontrolling a supply amount of reducing gas supplied from the fuelreformer into the exhaust channel, according to the oxygen concentrationthus detected by the oxygen concentration detection means.

According to this configuration, the supply amount of reducing gas iscontrolled according to the oxygen concentration in a vicinity of theNOx purification catalyst. This enables the exhaust air/fuel ratio ofexhaust flowing into the NOx purification catalyst to be adjustedappropriately, and thus the efficiency of the SOx regeneration processto be further improved.

Preferably, the fuel reformer produces reducing gas by way of a partialoxidation reaction of hydrocarbon fuel and air.

According to this configuration, this fuel reformer can be made asmaller size by producing reducing gas by way of a partial oxidationreaction. In order words, this is because a device to supply extraenergy from outside does not need to be provided since the partialoxidation reaction as described above is an exothermic reaction, andonce the reaction starts, the reaction progresses spontaneously. Inaddition, there is also no need to also provide a converter and systemfor concentrating hydrogen of a shift reaction, etc. Moreover, thelight-off time of the fuel reformer can be shortened by making the fuelreformer to be small in this way. Therefore, reducing gas can be quicklysupplied into the exhaust channel as needed.

Furthermore, by introducing light hydrocarbons generated secondarily inthis partial oxidation reaction to the NOx purification catalyst alongwith carbon monoxide and hydrogen, it can also be used in thepurification of SOx.

Preferably, the internal combustion engine uses light oil as fuel, andcombusts the fuel by way of compression ignition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of an internal combustionengine and an exhaust emission control device thereof according to afirst embodiment of the present invention;

FIG. 2 is a flowchart showing a sequence of a DPF regeneration processby an ECU according to the embodiment;

FIG. 3A is a graph showing an example of control of the DPF regenerationprocessing according to the embodiment;

FIG. 3B is a graph showing an example of control of the DPF regenerationprocess according to the embodiment;

FIG. 4 is a view showing a configuration of an internal combustionengine and an exhaust emission control device thereof according to asecond embodiment of the present invention;

FIG. 5 is a flowchart showing a sequence of a DPF regeneration processby an ECU according to the embodiment;

FIG. 6 is a view showing a configuration of an internal combustionengine and an exhaust emission control device thereof according to athird embodiment of the present invention;

FIG. 7 is a flowchart showing a sequence of a regeneration process by anECU according to the embodiment;

FIG. 8 is a graph showing a relationship between a PM deposition amounton the DPF and two threshold values used in the updating of flags; and

FIG. 9 is a graph showing a relationship between a SOx poisoning amountof the NOx purification catalyst and two threshold values used in theupdating of flags.

EXPLANATION OF REFERENCE NUMERALS

-   -   1 Engine (internal combustion engine)    -   4 Exhaust plumbing (exhaust channel)    -   5 Exhaust manifold (exhaust channel)    -   14 Inlet    -   14B Inlet    -   23 UEGO sensor (oxygen concentration detection means)    -   23B UEGO sensor (oxygen concentration detection means)    -   26B exhaust temperature sensor (catalyst temperature estimation        means)    -   27 Pressure differential sensor (deposition amount estimation        means)    -   28 NOx sensor (SOx poisoning amount estimation means)    -   29U Upstream temperature sensor (upstream exhaust temperature        detection means)    -   29D Downstream temperature sensor (downstream exhaust        temperature detection means)    -   31 Catalytic converter    -   32 DPF    -   33 NOx purification catalyst    -   40 Electronic control unit (regeneration means, target        concentration setting means, oxygen concentration control means)    -   40A Electronic control unit (regeneration means, normal        regeneration means, heated regeneration means, first heated        regeneration means, second heated regeneration means, combustion        determination means, filter temperature estimation means, torque        estimation means, and timing means)    -   40B Electronic control unit (regeneration means, exhaust        temperature control means, deposition amount estimation means,        SOx poisoning amount estimation means, catalyst temperature        estimation means, supply amount control means)    -   50 Fuel reformer    -   50B Fuel reformer

PREFERRED MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a view showing a configuration of an internal combustionengine and the exhaust emission control device thereof according to anembodiment of the present invention. An internal combustion engine(hereinafter referred to as “engine”) 1 is a diesel engine that directlyinjects fuel into the combustion chamber of each cylinder 7 and combuststhe fuel by way of compression ignition, and uses diesel oil as thefuel. In addition, a fuel injector, which is not illustrated, isprovided to each cylinder 7. These fuel injectors are electricallyconnected to an electronic control unit (hereinafter referred to as“ECU”) 40, and the valve-open duration and the valve-close duration ofthe fuel injectors, i.e. the fuel injection amount and fuel injectiontiming, are controlled by the ECU 40.

The engine 1 is provided with intake plumbing 2 in which intake airflows, exhaust plumbing 4 in which exhaust gas flows, an exhaust-gasrecirculation path 6 that recirculates a portion of the exhaust in theexhaust plumbing 4 to the intake plumbing 2, and a turbocharger 8 thatcompresses and feeds intake air to the intake plumbing 2.

The intake plumbing 2 is connected to the intake port of each cylinder 7of the engine 1 via a plurality of branches of an intake manifold 3. Theexhaust plumbing 4 is connected to the exhaust port of each cylinder 7of the engine 1 via a plurality of branches of an exhaust manifold 5.The exhaust-gas recirculation path 6 branches from the exhaust manifold5 and leads to the intake manifold 3.

The turbocharger 8 includes a turbine, which is not illustrated,provided to the exhaust plumbing 4, and a compressor, which is notillustrated, provided to the intake plumbing 2. The turbine is driven bythe kinetic energy of exhaust gas flowing in the exhaust plumbing 4. Thecompressor is rotationally driven by the turbine, and compresses andfeeds intake air into the intake plumbing 2. In addition, the turbine isprovided with a plurality of variable vanes, which are not illustrated,and is configured so that the turbine revolution number (revolutionspeed) can vary by way of causing the aperture of the variable vanes tochange. The vane aperture of the turbine is electromagneticallycontrolled by the ECU 40.

A throttle valve 9 that controls the intake air amount GA of the engine1 is provided inside the exhaust plumbing 2 at an upstream side of theturbocharger 8. This throttle valve 9 is connected to the ECU 40 via anactuator, and the aperture thereof is electromagnetically controlled bythe ECU 40. In addition, an intercooler 11 for cooling the intake aircompressed by the turbocharger 8 is provided in the intake plumbing 2 ata downstream side of the turbocharger 8.

The exhaust-gas recirculation path 6 connects the exhaust manifold 5 andthe intake manifold 3, and recirculates a portion of the exhaust emittedfrom the engine 1. An EGR cooler 12, which cools exhaust gas that isrecirculated, and an EGR valve 13 that controls the flow rate of exhaustgas being recirculated are provided in the exhaust-gas recirculationpath 6. The EGR valve 13 is connected to the ECU 40 via an actuator,which is not illustrated, and the valve aperture thereof iselectromagnetically controlled by the ECU 40.

A catalytic converter 31 and DPF 32 are provided from an upstream sidein this order downstream of the turbocharger 8 in the exhaust plumbing4.

The catalytic converter 31 includes a three-way catalyst thatcontinuously oxidizes reductive gas supplied from the fuel reformer 50described later. This catalytic converter 31 contains at least oneselected from the group consisting of platinum (Pt), palladium (Pd) andrhodium (Rh) as a noble metal active species in a catalytic combustionreaction such as of carbon monoxide, hydrogen and light hydrocarbonscontained in the reductive gas described below, and ceria (CeO₂), whichhas oxygen storage ability. By supplying reductive gas to such acatalytic converter 31, the temperature can be quickly raised even in astate in which the exhaust temperature is low. In addition, bycontaining ceria, stable catalyst action can be demonstrated, even undera sudden oxygen concentration fluctuation or the like.

In the present embodiment, a substance, which is prepared by producing aslurry by way of agitating and mixing 2.4 (g/L) of platinum, 1.2 (g/L)of rhodium, 6.0 (g/L) of palladium, 50 (g/L) of ceria, 150 (g/L) ofalumina (Al₂O₃), and 10 of binder along with an aqueous medium in a ballmill, then after coating this slurry on a support made of Fe—Cr—Alalloy, drying and calcining this at 600° C. over 2 hours, is used forthe catalytic converter 31.

The DPF 32 collects, when exhaust flows through the fine pores in thefilter walls, PM with elemental carbon as a main component in exhaust,by way of causing deposition thereof on the surface of the filter wallsand in the pores inside the filter walls. For example, a ceramic such assilicon carbide (SiC) and a metallic madreporic body is used as aconstituent material of the filter wall.

When PM is collected until the limit of the collection ability of theDPF 32, i.e. until the collection limit, since the pressure drop becomeslarge, it is necessary to appropriately perform the DPF regenerationprocess to cause the PM thus collected to combust. This DPF regenerationprocess is performed by raising the temperature of the exhaust flowinginto the DPF 32 up to the combustion temperature of the PM collected inthe DPF 32. A sequence of this DPF regeneration process is explained indetail with reference to FIG. 2 below.

In addition, a fuel reformer 50, which reforms fuel gas to produce areformed gas containing hydrogen (H₂), and carbon monoxide (CO) isconnected upstream of the catalytic converter 31 and DPF 32 inside theexhaust plumbing 4. This fuel reformer 50 supplies the reformed gas thusproduced into the exhaust plumbing 4 from an inlet 14 formed upstream ofthe catalytic converter 31 and DPF 32 inside the exhaust plumbing 4 asreductive gas.

The fuel reformer 50 is configured to include a gas path 51 thatconnects one end side to the exhaust plumbing 4, a fuel gas supplydevice 52 that supplies fuel gas from another end side of this gas path51, and a reforming catalyst 53 as a reforming catalyst provided in thegas path 51.

The fuel gas supply device 52 produces fuel gas by mixing fuel stored ina fuel tank and air supplied by the compressor at a predetermined ratio,and supplies this fuel gas to the gas path 51. This fuel gas supplydevice 52 is connected to the ECU 40, and a supply amount of fuel gasand a mixture ratio thereof are controlled by the ECU 40. In addition,it is made possible to control the supply amount GRG (amount of reducinggas supplied into the exhaust plumbing 4 per unit time) of reductive gassupplied to the exhaust plumbing 4 by controlling the supply amount ofthis fuel gas.

The reforming catalyst 53 contains rhodium and ceria. This reformingcatalyst 53 is a catalyst that reforms the fuel gas supplied from thefuel gas supply device 52, and produces a reformed gas containinghydrogen, carbon monoxide, and hydrocarbons. More specifically, thisreforming catalyst 53 produces reformed gas that is higher pressure thanatmospheric pressure and contains more carbon monoxide than hydrogen byvolume ratio by way of the partial oxidation reaction of hydrocarbonfuel constituting the fuel gas and air. In other words, the reformed gascontains more carbon monoxide than hydrogen. In addition, as describedabove, the partial oxidation reaction is an exothermal reaction. As aresult, the fuel reformer 50 is able to supply into the exhaust plumbing4 reducing gas of a temperature that is higher than the exhaust in thevicinity of the inlet 14 in the exhaust plumbing 4.

In addition, a heater (not illustrated) configured to include a glowplug, spark plug, or the like is connected to the reforming catalyst 53,whereby it is possible to heat the reforming catalyst 53 with startup ofthe fuel reformer 50. Moreover, the fuel reformer 50 is providedseparately from the exhaust plumbing 4. In other words, the fuel gassupply device 52 and reforming catalyst 53 of the fuel reformer 50 arenot provided in the exhaust plumbing 4.

An air-flow meter 21 that detects an intake air amount GA (air amountnewly aspirated into the engine 1 per unit time) of the engine 1, anexhaust temperature sensor 22 that detects a temperature TE of exhaustin the exhaust plumbing 4 flowing into the catalytic converter 31 andDPF 32, a UEGO sensor 23 that detects an oxygen concentration AF of theexhaust in the exhaust plumbing 4 flowing into the catalytic converter31 and the DPF 32, and a pressure sensor 26 that detects a pressure PEof exhaust on a downstream side of the DPF 32 in the exhaust plumbing 4are connected to the ECU 40, and detection signals of these sensors aresupplied to the ECU 40.

The ECU 40 includes an input circuit that has functions such as ofshaping input signal wave forms from every kind of sensor, correctingthe voltage levels to predetermined levels, and converting analog signalvalues to digital signal values, and a central processing unit(hereinafter referred to as “CPU”). In addition to this, the ECU 40includes a storage circuit that stores every kind of calculation programexecuted by the CPU and calculation results, and an output circuit thatoutputs control signals to the fuel reformer 50, throttle valve 9, EGRvalve 13, turbocharger 8, fuel injectors of the engine 1, and the like.

FIG. 2 is a flowchart showing a sequence of the DPF regeneration processby the ECU. As shown in FIG. 2, the DPF regeneration process makes itpossible to cause PM collected in the DPF to be combusted whilesupplying reductive gas produced by the fuel reformer into the exhaustplumbing 4.

In Step S1, it is determined whether a DPF regeneration request flagFDPFRR is “1”. In a case of this determination being YES, Step S2 isadvanced to, and in a case of being NO, this process ends immediately.Herein, when the consumed amount of fuel has reached a predeterminedvalue, or when a traveled distance of the vehicle has reached apredetermined value, this DPF regeneration request flag FDPFRR is set to“1”. In addition, upon being set to “1”, this DPF regeneration requestflag FDPFRR is returned to “0” by way of a process not illustrated,after a predetermined regeneration time has elapsed.

In Step S2, it is determined whether the engine is in an idle operatingstate. In a case of this determination being YES, Step S5 is advancedto, and in a case of being NO, Step S3 is advanced to.

In Step S3, it is determined whether the engine is in a decelerationoperating state. In a case of this determination being YES, Step S5 isadvanced to, and in a case of being NO, Step S4 is advanced to.

In Step S4, an oxygen concentration target value AFTV of exhaust flowinginto the DPF during DPF regeneration process execution is set based on afirst control map, which is not illustrated, and then Step S6 isadvanced to.

In Step S5, the oxygen concentration target value AFTV of exhaustflowing into the DPF during DPF regeneration process execution is setbased on a second control map, which is not illustrated, and then StepS6 is advanced to.

The first control map and the second control map respectively set thetarget value AFTV of the oxygen concentration AF of exhaust flowing intothe DPF, with at least one among a flow rate GE of exhaust flowing intothe DPF, the exhaust temperature TE detected by the exhaust temperaturesensor, and a PM deposition amount QPM deposited on the DPF as aparameter.

For example, in a case of including the exhaust flow rate GE as aparameter, the oxygen concentration target value AFTV is set so as tobecome lower as the exhaust flow rate GE decreases. In a case ofincluding the exhaust temperature TE as a parameter, the oxygenconcentration target value AFTV is set so as to become lower as theexhaust temperature TE rises. In addition, in a case of including the PMdeposition amount QPM as a parameter, it is set so as to become lower asthe PM deposition amount QPM increases.

Herein, if comparing the first control map and the second control map,the first control map sets the oxygen concentration target value AFTV toa concentration that is higher than the second control map.Specifically, in a case of using a parameter of the same value, theoxygen concentration target value set according to the first control mapwill be larger than the oxygen concentration target value set accordingto the second control map. In other words, in a case of being in an idleoperating state or deceleration operating state, the oxygenconcentration target value is set to a lower concentration.

It should be noted that, in Steps S4 and S5, the flow rate GE of exhaustflowing into the DPF is estimated based on the intake air amount GA, andthe PM deposition amount QPM is estimated based on the pressure PEdetected by the pressure sensor.

In Step S6, supply of reductive gas is started, and the supply amountGRG of reductive gas and the intake air amount GA are adjusted so thatthe oxygen concentration AF of exhaust flowing into the DPF matches theoxygen concentration target value AFTV thus set, and then this processends.

In addition, the supply amount GRG of reductive gas and the intake airamount GA are adjusted so that the exhaust air/fuel ratio of exhaustflowing into the DPF does not fall below the stoichiometric ratio.

FIGS. 3A and 3B are graphs showing examples of control of the above DPFregeneration process.

FIG. 3A shows time variation of the PM deposition amount QPM. In thisfigure, a time t₀ is set as a DPF regeneration process start time, andthe PM deposition amount QPM gradually reduces from this time t₀.

FIG. 3B is a graph showing time variation of the oxygen concentrationtarget value AFTV. In this figure, the solid line 91 indicates the timevariation of the oxygen concentration target value in a case of havingbeen set based on the first control map, and the solid line 92 indicatesthe time variation of the oxygen concentration target value in a case ofhaving been set based on the second control map. In addition, the timet₁ indicates a time at which an idle operating state was transition tofrom a normal operating state. As shown in FIG. 3B, the oxygenconcentration target value is determined based on the first control mapfrom when the DPF regeneration process is started at time t₀ until whenthe idle operating state is transitioned to at time t₁ (refer to Step S4of FIG. 2), and the oxygen concentration target value is determined tobe a lower concentration based on the second control map (refer to StepS5 of FIG. 2).

As explained in detail above, according to the present embodiment, thecatalytic converter 31 that continuously oxidizes reductive gas isprovided in the exhaust plumbing 4 between the DPF 32 and the inlet 14at which reductive gas produced by the fuel reformer 50 is supplied, anda regeneration process to cause PM to be combusted is executed whilesupplying reductive gas into the exhaust plumbing 4.

This enables the oxygen concentration of exhaust flowing into the DPF 32to be controlled irrespective of the operating state of the engine 1, bysupplying reductive gas into the exhaust plumbing 4. As a result, evenin a case in which the DPF 32 may melt such as during an idle operatingstate or fuel-cut state described above, this can be avoided by loweringthe oxygen concentration. This enables the regeneration process to bestably executed irrespective of the operating state of the engine 1.

In addition, by employing such a reductive gas, the temperature of theexhaust can be raised without supplying unburned fuel such as in exhaustinjection and post injection. This enables problems such as theoccurrence of coking, degradation and corrosion of the catalyst andcomponents of the exhaust channel, deterioration in fuel economy, andoccurrence of oil dilution as described above to be avoided.

In addition, the molecular diameters of carbon monoxide and hydrogencontained in the reductive gas are small compared to the particlediameters of the hydrocarbons supplied by exhaust injection and postinjection. As a result, even in a case of a great amount of PMdepositing on the DPF 32, it is possible to supply reductive gas alongwith oxygen to deep parts thereof. This can effectively promote thecombustion of PM.

In addition, by providing the fuel reformer 50 that supplies reductivegas to be separate from the exhaust plumbing 4, the DPF regenerationtime period can be decided independently of the state of the engine 1.Therefore, the DPF regeneration process can be suitable executed asneeded while always controlling the engine 1 to an optimal state. Inaddition, by providing the fuel reformer 50 to be separate from theexhaust plumbing 4, reductive gas can always be produced at optimumefficiency and this reductive gas can be supplied into the exhaustplumbing 4, irrespective of the operating state of the engine 1, oxygenconcentration and steam concentration of exhaust, etc.

On the other hand, in a case of providing the fuel reformer 50 insidethe exhaust plumbing 4, it is necessary to enlarge the fuel reformer soas to be able to operate without influencing the components,temperature, and flow rate of the exhaust; however, according to thepresent embodiment, it is possible to perform operation stably withoutenlarging the device by providing the fuel reformer 50 to be separatefrom the exhaust plumbing 4. In addition, by providing the fuel reformer50 to be separate from the exhaust plumbing 4, it becomes possible toactivate the reforming catalyst 53 provided to the fuel reformer 50 atan early stage, by performing control of an independent system from thecontrol of the engine 1.

Furthermore, according to the present embodiment, the catalyticconverter 31 contains at least one selected from the group consisting ofplatinum, palladium, and rhodium. By containing these active species,the catalytic combustion reaction such as of hydrogen, carbon monoxide,and light hydrocarbons contained in the reductive gas can be promoted.

In addition, according to the present embodiment, an oxygenconcentration detection means is provided for detecting the oxygenconcentration of exhaust flowing into the DPF 32. This enables theoxygen concentration of exhaust flowing into the DPF 32 to be controlledto a predetermined target value with good accuracy. Moreover, bycontrolling the oxygen concentration of exhaust flowing into the DPF 32,an excessive rise in temperature of the DPF 32 during execution of theregeneration process can be prevented.

Furthermore, according to the present embodiment, more carbon monoxidethan hydrogen is contained in the reductive gas. Carbon monoxidecombusts at a lower temperature than hydrogen. Particulates deposited onthe particulate filter can be effectively combusted by supplying such areducing gas containing carbon monoxide.

In addition, according to the present embodiment, reductive gas issupplied at a temperature higher than the temperature of exhaust flowingthrough the exhaust plumbing 4 at the inlet 14. This enables thecombustion of PM to be promoted by causing the temperature of theexhaust flowing into the catalytic converter 31 to rise.

Moreover, according to the present embodiment, while executing theregeneration process, the oxygen concentration of exhaust flowing intothe DPF 32 is controlled so as to match a target oxygen concentration byadjusting at least one among the intake air amount, exhaustrecirculation ratio, fuel injection amount, and supply amount ofreductive gas. This enables the oxygen concentration of exhaust to bemade to match the target oxygen concentration with good accuracy.

In addition, according to the present embodiment, the oxygenconcentration target value is set based on at least one among the flowrate of exhaust flowing through the exhaust plumbing 4, the temperatureof exhaust, and the deposition amount of PM deposited on the DPF 32.This enables the target oxygen concentration to be set so that PM ismade to combust at an adequate temperature.

Moreover, according to the present embodiment, in a case of the engine 1being in an idle operating state, the oxygen concentration target valueis set to be low compared to a case of not being in an idle operatingstate. With this, even in a case in which the oxygen concentration inexhaust increases with the engine 1 having transitioned to an idleoperating state, the oxidation reaction in the DPF 32 is suppressed bysetting the oxygen concentration target value to be low, and thus anexcessive rise in temperature of this DPF 32 can be prevented.

In addition, according to the present embodiment, in a case of theengine 1 being in a deceleration operating state, the oxygenconcentration target value is set to be low compared to a case of notbeing in a deceleration operating state. With this, even in a case inwhich the oxygen concentration in exhaust increases with the engine 1transitioning to a deceleration operating state and decelerationfuel-cut having been performed, the oxidation reaction in the DPF 32 issuppressed by setting the oxygen concentration target value to be low,and thus an excessive rise in temperature of this DPF 32 can beprevented.

Furthermore, according to the present embodiment, this fuel reformer 50can be made a smaller size by producing the reductive gas by way of thepartial oxidation reaction. In order words, this is because a device tocontinually supply extra energy from outside does not need to beprovided since the partial oxidation reaction as described above is anexothermic reaction, and once the reaction starts, the reactionprogresses spontaneously. In addition, there is also no need to alsoprovide a converter and system for concentrating hydrogen of a shiftreaction, etc. Moreover, the light-off time of the fuel reformer 50 canbe shortened by making the fuel reformer 50 to be small in this way.Therefore, reductive gas can be quickly supplied into the exhaustplumbing 4 as needed.

Furthermore, by introducing light hydrocarbons generated secondarily inthis partial oxidation reaction to the catalytic converter 31 along withcarbon monoxide and hydrogen, it can also be used in raising thetemperature of exhaust.

According to the present embodiment, the ECU 40 configures theregeneration means, target concentration setting means, and oxygenconcentration control means. More specifically, the means related toSteps S1 to S6 of FIG. 2 correspond to the regeneration means, the meansrelated to Steps S4 and S5 correspond to the target concentrationsetting means, and the means related to Step S6 corresponds to theoxygen concentration control means.

It should be noted that various modifications are possible to theaforementioned embodiment.

For example, although the catalytic converter 31 having an oxidativefunction of continuously oxidizing reductive gas was provided in theexhaust plumbing 4 on an upstream side of the DPF 32 in theabove-mentioned embodiment, it is not limited thereto. For example, asimilar catalyst having an oxidative function may be supported on theDPF, without providing the catalytic converter to be separate from theDPF. In addition, in this case, it is preferable for the catalystsupported on the DPF to contain at least one selected from the groupconsisting of palladium, rhodium, platinum, silver, and gold.

This enables the following effects to be exerted in addition to theeffects of the above-mentioned embodiment. In other words, by supportinga catalyst having an oxidative function on the DPF, the exhaust emissioncontrol device can be made compact, and the combustion reaction of PMcan be further promoted. Therefore, the time from supplying reductivegas until combustion of PM begins can be further shortened.

Moreover, in the above-mentioned embodiment, although the supply amountGRG of reductive gas and the intake air amount GA are adjusted so thatthe oxygen concentration AF of exhaust flowing into the DPF matches theoxygen concentration target value AFTV that has been set in Step S6, itis not limited thereto. The exhaust recirculation ratio, fuel injectionamount of the engine, and the like may be adjusted in addition to thesupply amount GRG of reductive gas and the intake air amount GA.

Second Embodiment

A second embodiment of the present invention is explained below whilereferring to the drawings. In the explanation of the second embodimentbelow, constitutional requirements identical to the first embodiment areassigned the same reference symbol, and explanations thereof are omittedor simplified.

FIG. 4 is a view showing a configuration of an engine 1 and an exhaustemission control device thereof according to the second embodiment ofthe present invention. The second embodiment is mainly different fromthe first embodiment in the configuration of an ECU 40A.

An upstream temperature sensor 29U that detects an exhaust temperatureTU in the exhaust plumbing 4 on an upstream side of the DPF 32 and thecatalytic converter 31, and a downstream temperature sensor 29D thatdetects an exhaust temperature TD in the exhaust plumbing 4 on adownstream side of the DPF 32 are connected to the ECU 40A, anddetection signals of these sensors are supplied to the ECU 40A.

FIG. 5 is a flowchart showing a sequence of a DPF regeneration processby the ECU. As shown in FIG. 5, in the DPF regeneration process, anormal regeneration process that executes the regeneration processwithout employing reductive gas supplied by the fuel reformer, and aheated regeneration process that allows execution of the regenerationprocess employing reductive gas become switchable according topredetermined conditions. In addition, this DPF regeneration process isperformed every predetermined time period, for example.

In Step S11, it is determined whether the DPF regeneration request flagFDPFRR is “1”. In a case of this determination being YES, Step S12 isadvanced to, an in a case of being NO, this process ends immediately.Herein, when the consumed amount of fuel has reached a predeterminedvalue, or when a traveled distance of the vehicle has reached apredetermined value, this DPF regeneration request flag FDPFRR is set to“1”.

In Step S12, it is determined whether the exhaust temperature TD on adownstream side of the DPF detected by the downstream temperature sensoris lower than a predetermined judgment temperature TATH, and in a caseof this determination being YES, it is determined that the PM depositedon the DPF is not in a combusted state, and Step S14 is advanced to,whereas in a case of being NO, it is determined that PM is in acombusted state, and Step S13 is advanced to.

In Step S13, the normal regeneration process is executed, and then StepS19 is advanced to. In this normal regeneration process, for example,the temperature of exhaust is made to rise up to the combustiontemperature of PM by executing post injection.

In Step S14, the temperature TTWC of the catalytic converter isestimated based on the exhaust temperature TU upstream of the catalyticconverter detected by the upstream temperature sensor, it is determinedwhether this catalytic converter temperature TTWC is lower than apredetermined judgment temperature TBTH, and in a case of thisdetermination being YES, Step S17 is advanced to, whereas in a case ofbeing NO, Step S15 is advanced to.

In Step S15, it is determined whether the engine is in a low-loadoperating state, and in a case of this determination being YES, Step S17is advanced to, whereas in a case of being NO, Step S16 is advanced to.More specifically, a generated torque TRQ of the engine is estimated,and it is determined whether the engine is in a low-load operating stateby determining whether this generated torque TRQ is less than apredetermined torque judgment value TRQTH. In addition, in the presentembodiment, the generated torque TRQ of the engine is estimated based onat least one among the revolution speed of the engine, fuel injectionamount, and fuel injection timing.

In Step S16, it is determined whether it is immediately after startup,and in a case of this determination being YES, Step S17 is advanced to,whereas in a case of being NO, Step S18 is advanced to. Herein, thisdetermination as to whether being immediately after startup is performedbased on whether the elapsed time TIM since startup of the engine thatis measured by a timer, which is not illustrated, is less than apredetermined judgment time TIMTH.

In Step S17, execution of a first heated regeneration process isstarted, and then Step S19 is advanced to. In this first heatedregeneration process, reductive gas produced by the fuel reformer issupplied into the exhaust plumbing along with the intake air amount GAbeing reduced to a predetermined amount by closing the throttle valve.

In addition, in Step S18, execution of a second heated regenerationprocess is started, and then Step S19 is advanced to. In this secondheated regeneration step, the intake air amount GA is reduced to apredetermined amount by closing the throttle valve. Moreover, in thissecond heated regeneration process, supply of reductive gas is notperformed.

In Step S19, it is determined whether a predetermined regeneration timehas elapsed. In a case of this determination being YES, Step S20 isadvanced to and this process ends after the DPF regeneration requestflag is returned to “0”, whereas in a case of being NO, this processends immediately.

As described above in detail, according to the present embodiment, whenexecuting the DPF regeneration process in which PM collected in the DPF32 is caused to combust, the normal regeneration process that executesthe regeneration process without employing reductive gas and the firstand second heated regeneration processes that allow execution of theregeneration processing employing reductive gas are switched accordingto predetermined conditions. Herein, molecules that easily combust suchas hydrogen and carbon monoxide are contained in the reductive gasproduced by the fuel reformer 50. Even in a state in which the exhausttemperature is low and it is difficult to cause PM to combust, thetemperature of exhaust can be quickly raised by supplying such areductive gas to the DPF 32, for example.

In addition, by switching between the normal regeneration process andfirst and second heated regeneration processes according topredetermined conditions, for example, a regeneration process can beexecuted even if it enters a state in which a DPF regeneration processwould be difficult to execute by a conventional method as describedabove, such as in a case of immediately after engine startup or havingtransitioned to low-load operation. In other words, it is possible toreduce the frequency at which the operating state of the engine enters asituation in which it is difficult to continue the DPF regenerationprocess, thereby forcing interruption of the regeneration process.Therefore, the time required in the regeneration process can beshortened.

In addition, by employing such a reductive gas, the temperature ofexhaust can be made to rise without supplying unburned fuel as in theexhaust injection and post injection. This enables problems such as theoccurrence of coking, degradation and corrosion of the catalyst andcomponents of the exhaust channel, deterioration in fuel economy, andoccurrence of oil dilution as described above to be avoided.

In addition, the molecular diameters of carbon monoxide and hydrogencontained in the reductive gas are small compared to the moleculardiameters of the hydrocarbons supplied by exhaust injection and postinjection. As a result, even in a case of a great amount of PMdepositing on the DPF 32, it is possible to supply reductive gas alongwith oxygen to deep parts thereof. This can efficiently promote thecombustion of PM.

In addition, by providing the fuel reformer 50 that supplies reductivegas to be separate from the exhaust plumbing 4, the regeneration timeperiod of PM can be decided independently of the state of the engine 1.Therefore, the DPF regeneration process can be suitable executed asneeded while always controlling the engine 1 to an optimal state. Inaddition, by providing the fuel reformer 50 to be separate from theexhaust plumbing 4, reductive gas can always be produced at optimumefficiency and this reductive gas can be supplied into the exhaustplumbing 4, irrespective of the operating state of the engine 1, oxygenconcentration and steam concentration of exhaust, etc.

On the other hand, in a case of providing the fuel reformer 50 insidethe exhaust plumbing 4, it is necessary to enlarge the fuel reformer 50so as to be able to operate without influencing the components,temperature, and flow rate of the exhaust; however, according to thepresent embodiment, it is possible to perform operation stably withoutenlarging the device by providing the fuel reformer 50 to be separatefrom the exhaust plumbing 4. In addition, by providing the fuel reformer50 to be separate from the exhaust plumbing 4, it becomes possible toactivate the reforming catalyst 53 of the fuel reformer 50 at an earlystage, by performing control of an independent system from the controlof the engine 1.

Furthermore, according to the present embodiment, more carbon monoxidethan hydrogen is contained in the reductive gas. Carbon monoxidecombusts at a lower temperature than hydrogen. PM deposited on the DPF32 can be efficiently combusted by supplying such a reductive gascontaining carbon monoxide.

In addition, according to the present embodiment, the reductive gasproduced by the fuel reformer 50 flows into the catalytic converter 31and combusts by way of this catalytic converter 31. By combustingreductive gas by way of the catalytic converter 31 in this way, thetemperature of exhaust is raised, and PM deposited on the DPF 32 can beefficiently combusted.

Moreover, according to the present embodiment, in a case of havingdetermined that the PM deposited on the DPF 32 is in a combusted state,the normal regeneration process is executed, and in a case of havingdetermined that the PM is not in a combusted state, the first heatedregeneration process or the first heated regeneration process isexecuted. This enables the regeneration process to be efficientlyexecuted while preventing the reductive gas from being consumed for nopurpose. In addition, this enables the time required for theregeneration process to be shortened according to the operating state ofthe engine or the like.

Moreover, according to the present embodiment, it is determined whetherthe PM is in a combusted state based on the exhaust temperature on adownstream side of the DPF 32. This enables the combusted state of PM tobe determined with good accuracy.

Furthermore, according to the present embodiment, in a case of executingthe first or second heated regeneration process, the intake air amountof the engine 1 is reduced compared to a case of executing the normalregeneration process. As such, the temperature of the DPF 32 can bequickly raised by executing the first or second heated regenerationprocess.

In addition, according to the present embodiment, in a case of thetemperature TTWC of the catalytic converter 31 being lower than thepredetermined judgment temperature TBTH, the first heated regenerationprocess is executed. With this, even in a state in which the exhausttemperature is low and it is difficult to cause PM to combust, theexhaust temperature is quickly raised, and thus combustion of PM can bepromoted.

In addition, according to the present embodiment, in a case of thegenerated torque TRQ being lower than the predetermined judgment valueTRQTH, the first heated regeneration process is executed. With this,even in a state in which the engine 1 is in a low-load operating stateand it is difficult to cause PM to combust, the exhaust temperature isquickly raised, and thus the combustion of PM can be promoted.

Moreover, according to the present embodiment, in a case of the elapsedtime TIM from starting up the engine 1 is less than the predeterminedjudgment time TIMTH, the first heated regeneration process is executed.With this, even in a case of not being long after startup of the engine1 and it being difficult to cause PM to combust, the exhaust temperatureis quickly raised, and thus the combustion of PM can be promoted.

In the present embodiment, the ECU 40A configures a regeneration means,normal regeneration means, heated regeneration means, first heatedregeneration means, second heated regeneration means, combustionjudgment means, a portion of a filter temperature estimation means, aportion of a torque estimation means, and a timing means. Morespecifically, the means related to Steps S11 to S20 of FIG. 5 correspondto the regeneration means, the means related to Step S13 correspond tothe normal regeneration means, the means related to Steps S17 and S18correspond to the heated regeneration means, the means related to StepS17 correspond to the first heated regeneration means, the means relatedto Step S18 correspond to the second heated regeneration means, themeans related to Step S12 and the downstream temperature sensor 29Dcorrespond to the combustion judgment means, the means related to StepS15 correspond to the torque estimation means, and the means related toStep S16 correspond to the timing means.

It should be noted that various modifications are possible to theaforementioned embodiment.

For example, although the catalytic converter 31 having an oxidativefunction of continuously oxidizing reductive gas was provided in theexhaust plumbing 4 on an upstream side of the DPF 32 in theabove-mentioned embodiment, it is not limited thereto. For example, asimilar catalyst having an oxidative function may be supported on theDPF, without providing the catalytic converter to be separate from theDPF. With this, compared to a case in which the catalytic converter andthe DPF are provided separately, the exhaust emission control device canbe made compact, and the combustion reaction of PM can be furtherpromoted. Therefore, the time from supplying reductive gas untilcombustion of PM beings can be further shortened.

Moreover, in the above-mentioned embodiment, although it was determinedwhether the PM deposited on the DPF is in a combusted state based on theexhaust temperature TD on a downstream side of the DPF detected by thedownstream temperature sensor 29D in Step S12, it is not limitedthereto. For example, an oxygen concentration detection means fordetecting or estimating the oxygen concentration of exhaust on adownstream side of the DPF may be provided, and it may be determinedwhether the PM is in a combusted state based on the oxygen concentrationdetected or estimated by this oxygen concentration detection means.Effects similar to the above-mentioned embodiment can be exerted also ifconfigured in this way.

For example, in the above-mentioned embodiment, although determinationof whether to execute the first heated regeneration process or toexecute the second heated regeneration process was performed based onthe temperature of the catalytic converter, the operating state of theengine, and the elapsed time from beginning startup of the engine inSteps S14 to S16, it is not limited thereto. For example, in a case ofthe exhaust temperature TU detected by the upstream temperature sensorbeing lower than a predetermined judgment temperature TCTH, it may beconfigured so as to execute the first heated regeneration process. Inaddition, a filter temperature estimation means for estimating atemperature TDPF of the DPF may be provided, for example, and it may beconfigured so as to execute the first heated regeneration process in acase in which the DPF temperature TDPF estimated by this filtertemperature estimation means is lower than a predetermined judgmenttemperature TDTH. Effects similar to the above-mentioned embodiment canbe exerted also if configured in this way.

In addition, in the above-mentioned embodiment, although the intake airamount GA is reduced to a predetermined amount by closing the throttlevalve in Step S17 and Step S18, when executing the first heatedregeneration process and the second regeneration process, it is notlimited thereto. These processes are not limited to reduction of theintake air amount, and it may be configuration to increase the exhaustrecirculation flow rate by opening the EGR valve or to lower thecharging efficiency of the engine. Effects similar to theabove-mentioned embodiment can be exerted also if configured in thisway.

Third Embodiment

A third embodiment of the present invention is explained below whilereferring to the drawings. In the explanation of the third embodimentbelow, constitutional requirements identical to the first embodiment areassigned the same reference symbol, and explanations thereof are omittedor simplified.

FIG. 6 is a view showing a configuration of an engine 1 and an exhaustemission control device thereof according to the third embodiment of thepresent invention. In addition to the configuration of the fuel reformer50B and the configuration of the ECU 40B, the third embodiment is mainlydifferent from the first embodiment in the aspect of providing a NOxpurification catalyst 33.

The catalytic converter 31, DPF 32, and NOx purification catalyst 33 areprovided in this sequence from an upstream side in the exhaust plumbing4.

The NOx purification catalyst 33 includes platinum (Pt) that acts as acatalyst and is supported on a carrier of alumina (Al₂O₃), ceria (CeO₂),and a complex oxide of cerium and a rare earth (hereinafter referred toas “ceria-based complex oxide”), a ceria or a ceria-based complex oxidehaving NOx adsorption capacity, and a zeolite having a function ofretaining ammonia (NH₃) generated on the catalyst as ammonium ion (NH₄⁺).

In the present embodiment, a material formed by loading a NOx reductioncatalyst composed of two layers onto a catalyst support is used as theNOx purification catalyst 33.

The lower layer of the NOx reduction catalyst is formed by producing aslurry by placing a material constituted with 4.5 (g/L) of platinum, 60(g/L) of ceria, 30 (g/L) of alumina, 60 (g/L) of Ce—Pr—La—Ox, and 20(g/L) of Zr—Ox into a ball mill with an aqueous medium, then agitatingand mixing, followed by coating this slurry on the catalyst support.

In addition, the upper layer of the NOx reduction catalyst is formed byproducing a slurry by placing a material constituted with 75 (g/L) of abeta zeolite ion-exchanged with iron (Fe) and cerium (Ce), 7 (g/L) ofalumina, and 8 (g/L) of a binder into a ball mill with an aqueousmedium, then agitating and mixing, followed by coating this slurry onthe lower layer described above.

When the amount of adsorbed ammonia of the NOx purification catalyst 33is small, since the NOx purification ability decreases, supply of areducing agent (hereinafter referred to as “reduction”) to the NOxpurification catalyst 33 is performed in order to reduce the NOxappropriately. With this reduction, the reducing agent is supplied tothe NOx purification catalyst 33 by making the air/fuel ratio (engineair/fuel ratio) of the mixture inside the combustion chamber of theengine 1 to be richer than the stoichiometric ratio. In other words, byenriching the exhaust air/fuel ratio emitted from the engine 1, theconcentration of reducing agent in the exhaust flowing into the NOxpurification catalyst 33 becomes higher than the concentration ofoxygen, thereby carrying out reduction.

Purification of NOx in this NOx purification catalyst 33 will beexplained.

First, the engine air/fuel ratio is set to be leaner thanstoichiometric, and when so-called lean burn operation is performed, theconcentration of reducing agent in the exhaust flowing into the NOxpurification catalyst 33 becomes lower than the concentration of oxygen.As a result thereof, nitrogen monoxide (NO) and oxygen (O₂) in theexhaust react by action of the catalyst, and is adsorbed to ceria or aceria-based complex oxide as NO₂. In addition, carbon monoxide (CO) thathas not reacted with oxygen is also adsorbed to ceria or the ceria-basedcomplex oxide.

Next, so-called rich operation is performed in which the engine air/fuelratio is set to be richer than stoichiometric, and the exhaust air/fuelratio is enriched. In other words, when reduction to make theconcentration of the reducing agent in the exhaust higher than theconcentration of oxygen is carried out, carbon dioxide (CO₂) andhydrogen (H₂) are generated by carbon monoxide in the exhaust reactingwith water (H₂O), and carbon monoxide (O) and carbon dioxide (CO₂) aswell as hydrogen are generated by hydrocarbons (HO) in the exhaustreacting with water. Furthermore, NOx contained in the exhaust and NOx(NO, NO₂) adsorbed to ceria or the ceria-based complex oxide (andplatinum) react with the hydrogen thus generated by action of thecatalyst, thereby generating ammonia (NH₃) and water. In addition, theammonia thus generated here is adsorbed to zeolite in the form ofammonium ions (NH₄ ⁺).

Next, lean burn operation is performed in which the engine air/fuelratio is set to be leaner than stoichiometric, and when theconcentration of the reducing agent in the exhaust flowing into the NOxpurification catalyst 33 is set to be lower than the concentration ofoxygen, NOx is adsorbed to ceria or the ceria-based complex oxide.Furthermore, in a state where ammonium ions are adsorbed to the zeolite,NOx and oxygen in the exhaust react with ammonia, thereby generatingnitrogen (N₂) and water.

In this way, according to the NOx purification catalyst 33, ammoniagenerated during reducing agent supply is adsorbed to the zeolite, andthe ammonia adsorbed during lean burn operation reacts with NOx;therefore, it is possible to perform purification of NOx efficiently.

When SOx in exhaust is absorbed to the NOx purification catalyst 33, theNOx purification performance of the NOx purification catalyst 33declines. As a result, it is necessary to perform a SOx regenerationprocess to purify the SOx absorbed to the NOx purification catalyst 33.More specifically, by way of the regeneration process, which isexplained in detail referring to FIG. 7, the exhaust flowing into theNOx purification catalyst 33 is made a reducing atmosphere and this NOxpurification catalyst 33 is raised in temperature thereby.

In the present embodiment, the fuel reformer 50B is connected in theexhaust plumbing 4 between the DPF 32 and the NOx purification catalyst33. In other words, the reductive gas produced by the fuel reformer 50Bis supplied from an inlet 14B formed in the exhaust plumbing 4 betweenthe DPF 32 and the NOx purification catalyst 33 into the exhaustplumbing 4.

A UEGO sensor 23B that is set in a vicinity of the NOx purificationcatalyst 33 and detect an oxygen concentration of the exhaust in theexhaust plumbing 4 between the inlet 14 and the NOx purificationcatalyst 33, i.e. exhaust air/fuel ratio AFB, an exhaust temperaturesensor 26B that detects a temperature TEB of exhaust in the exhaustplumbing 4 between the inlet 14B and the NOx purification catalyst 33, adifferential pressure sensor 27 that detects a pressure differential ΔPbetween an upstream side and a downstream side of the DPF 32, and a NOxsensor 28 that detects a NOx concentration DND of exhaust in the exhaustplumbing 4 on a downstream side of the NOx purification catalyst 33 areconnected to the ECU 40B, and detection signals of these sensors aresupplied to the ECU 40B.

The engine 1 is normally operated by setting the engine air/fuel ratioto be leaner than the stoichiometric ratio, and in a case in which PMdeposited on the DPF 32 is caused to combust or in a case in which SOxadsorbed to the NOx purification catalyst is purified, the regenerationprocess is performed.

The regeneration process of the present embodiment will be explainedwith reference to FIGS. 7 to 9.

FIG. 7 is a flowchart showing a sequence of the regeneration process bythe ECU. As shown in FIG. 7, in the regeneration process of the presentembodiment, the normal regeneration operation that performs a DPFregeneration process in which the DPF is raised in temperature byexecuting a reduction in the intake air amount and post injection,whereby PM collected on the DPF is caused to combust (Steps S32 to S39),and the simultaneous regeneration operation that performs a SOxregeneration process in which SOx adsorbed to the NOx purificationcatalyst is purified by supplying reductive gas while executing thisnormal regeneration operation (Steps S35 to S37) become selectivelyexecutable according to predetermined conditions.

In addition, in the regeneration process shown in FIG. 7, a normalregeneration execution request flag FDPFRP, a normal regeneration endrequest flag FDPFRE, a simultaneous regeneration execution request flagFSIMRP, and a simultaneous regeneration end request flag FSIMRE, whichrequest the execution or end of this normal regeneration operation andsimultaneous regeneration operation, are employed.

FIG. 8 is a graph showing a relationship of a deposition amount QPM ofPM on the DPF with a first threshold value QPMATH and a second thresholdvalue QPMBTH, which are used in updating the normal regenerationexecution request flag FDPFRP and the normal regeneration end requestflag FDPFRE. Herein, these two threshold values are set so thatQPMATH>QPMBTH.

If the engine operates continuously, the PM deposition amount QPM willincrease. Consequently, the normal regeneration execution request flagFDPFRP that requests execution of the normal regeneration operation isset to “1” in response to the PM deposition amount QPM having become atleast the first threshold value QPMATH.

Next, if the normal regeneration operation is executed, the PMdeposition amount QPM will decrease. Consequently, the normalregeneration end request flag FDPRRE that requests to end the normalregeneration operation is set to “1” in response to the PM depositionamount QPM having dropped below the second threshold value QPMBTH.

It should be noted that, in the present embodiment, the PM depositionamount QPM is estimated based on the differential pressure ΔP between anupstream side and a downstream side of the DPF detected by thedifferential pressure sensor.

FIG. 9 is a graph showing a relationship of a SOx poisoning amount QSOof the NOx purification catalyst with a first threshold value QSOATH anda second threshold value QSOBTH, which are used in updating thesimultaneous regeneration execution request flag FSIMRP and thesimultaneous regeneration end request flag FSIMRE. Herein, these twothreshold values are set so that QSOATH>QSOBTH.

If the engine operates continuously, the SOx poisoning amount QPM willincrease. Consequently, the simultaneous regeneration execution requestflag FSIMRP that requests execution of the simultaneous regenerationoperation is set to “1” in response to the SOx poisoning amount QSOhaving become at least the first threshold value QSOATH.

Next, if the simultaneous regeneration operation is executed, the SOxpoisoning amount QSO will decrease. Consequently, the simultaneousregeneration end request flag FSIMRE that requests to end thesimultaneous regeneration operation is set to “1” in response to the SOxpoisoning amount QSO having dropped below the second threshold valueQSOBTH.

It should be noted that, in the present embodiment, the SOx poisoningamount of the NOx purification catalyst is estimated based on the NOxconcentration DND of exhaust on a downstream side of the NOxpurification catalyst detected by the NOx sensor.

In addition, the normal regeneration execution request flag FDPFRP,normal regeneration end request flag FDPFRE, simultaneous regenerationexecution request flag FSIMRP, and simultaneous regeneration end requestflag FSIMRE are constantly updated with the PM deposition amount QPM andthe SOx poisoning amount QSO by the ECU.

Referring again to FIG. 7, in Step S31, it is determined whether eitherof the normal regeneration execution request flag FDPFRP or thesimultaneous regeneration execution request flag FSIMRP is “1”. In acase of this determination being YES, Step S32 is advanced to, and in acase of being NO, this process ends immediately.

In Step S32, intake air amount reduction control and post injectioncontrol are executed, and Step S33 is advanced to. With this intake airamount reduction control, the temperature of the exhaust is controlledby adjusting the intake air amount. More specifically, the throttlevalve is controlled and the intake air amount GA is reduced to apredetermined set amount, whereby the exhaust temperature is made torise. In addition, with the post injection control, post injection isexecuted, with the post injection amount being adjusted to apredetermined set amount.

In Step S33, it is determined whether the simultaneous regenerationexecution request flag FSIMRP is “1”. In a case of this determinationbeing YES, Step S34 is advanced to, and in a case of being NO, Step S36is advanced to.

In Step S34, a temperature TLNC of the NOx purification catalyst isestimated based on the exhaust temperature TEE detected by the exhausttemperature sensor, and it is determined whether this catalysttemperature TLNC is at least a predetermined temperature judgment valueTLNCTH. In a case of this determination being YES, Step S35 is advancedto, and in a case of being NO, Step S36 is advanced to.

In Step S35, reductive gas supply control is executed, i.e. thesimultaneous regeneration operation is executed, and then Step S36 isadvanced to. More specifically, the supply of reductive gas produced bythe fuel reformer into the exhaust plumbing is started, with the supplyamount of reductive gas being controlled based on an exhaust air/fuelratio AFB detected by the UEGO sensor.

Herein, it is also preferable for oxygen to be contained in the exhaustflowing through this exhaust plumbing when supplying reductive gas intothe exhaust plumbing.

In Step S36, it is determined whether the simultaneous regeneration endrequest flag FSIMRE is “1”. In a case of this determination being YES,Step S37 is advanced to, and in a case of being NO, Step S38 is advancedto.

In Step S37, reductive gas supply control ends, i.e. the simultaneousregeneration operation ends, the simultaneous regeneration executionrequest flag FSIMRP and the simultaneous regeneration end request flagFSIMRE return to “0”, and Step S38 is advanced to.

In Step S38, it is determined whether the normal regeneration endrequest flag FDPFRE is “1”. In a case of this determination being YES,Step S39 is advanced to, and in a case of being NO, this process ends.

In Step S39, the intake air amount reduction control and post injectioncontrol end, and the normal regeneration execution request flag FDPFRPand the normal regeneration end request flag FDPFRE return to “0”.

As described in detail above, according to the present embodiment, theDPF 32 was provided in the exhaust plumbing 4 on an upstream side of theNOx purification catalyst 33, and the fuel reformer 50B was providedthat supplies reductive gas containing hydrogen and carbon monoxide fromthe inlet 14B provided between this NOx purification catalyst 33 andthis DPF 32. With this, the exhaust air/fuel ratio of exhaust flowinginto the NOx purification catalyst 33 is kept low and the SOxregeneration process of the NOx purification catalyst 33 can be executedwith high efficiency by supplying reductive gas from downstream of theDPF 32, while the oxygen concentration of exhaust flowing into the DPF32 is kept high, and the DPF regeneration process is executed with highefficiency. In this way, according to the present embodiment, it ispossible to execute the DPF regeneration process and the SOxregeneration process simultaneously with high efficiency. Therefore, thetime required in these processes is shortened, which can improve fueleconomy, whereby degradation to the DPF 32 and the NOx purificationcatalyst 33 can also be reduced.

In addition, by providing the fuel reformer 50B to be separate from theexhaust plumbing 4, reductive gas can be supplied without increasing theheat capacity upstream of the NOx purification catalyst 33. This enablesthe SOx regeneration process to be executed without reducing the NOxpurification performance when at low temperature such as immediatelyafter startup of the engine 1.

Moreover, by providing the fuel reformer that produces reductive gas tobe separate from the exhaust channel, the execution time period of theSOx regeneration process can be decided independently of the state ofthe internal combustion engine. Therefore, the SOx regeneration processcan be suitable executed as needed while always controlling the engine 1to an optimal state. In addition, by providing the fuel reformer 50B tobe separate from the exhaust plumbing 4, reductive gas can always beproduced at optimum efficiency and this reductive gas can be suppliedinto the exhaust plumbing 4, irrespective of the operating state of theengine 1, the oxygen concentration or steam concentration of theexhaust, etc.

On the other hand, in a case of providing the fuel reformer 50B insidethe exhaust plumbing 4, it is necessary to enlarge the fuel reformer 50Bso as to be able to operate without influencing the components,temperature, and flow rate of the exhaust; however, according to thepresent embodiment, it is possible to perform operation stably withoutenlarging the device by providing the fuel reformer 50B to be separatefrom the exhaust plumbing 4. In addition, by providing the fuel reformer50B to be separate from the exhaust plumbing 4, it becomes possible toactivate the reforming catalyst 53 at an early stage by performingcontrol of an independent system from the control of the engine 1.

In addition, according to the present embodiment, more carbon monoxidethan hydrogen is contained in the reductive gas by volume ratio.Moreover, the temperature at which carbon monoxide begins to combust onthe catalyst is a temperature lower than the temperature at whichhydrogen begins to combust. The NOx purification catalyst 33 is quicklyraised in temperature by supplying such a reductive gas containingcarbon monoxide, and thus the purification of SOx can be promoted in theSOx regeneration process. In addition, reductive gas thus produced canbe supplied into the exhaust plumbing 4 without adding an extra deviceby producing reductive gas of a pressure higher than atmospheric.

Moreover, according to the present embodiment, reductive gas of atemperature higher than the temperature of exhaust flowing through theexhaust plumbing 4 at the inlet 14B is supplied. This enables the NOxpurification catalyst 33 to be quickly raised in temperature, and thusthe purification of SOx to be promoted in the SOx regeneration process.

In addition, according to the present embodiment, the normalregeneration operation that performs the DPF regeneration process andthe simultaneous regeneration operation that supplies reductive gas andperforms the SOx regeneration process while executing this normalregeneration operation are selectively executed according topredetermined conditions. This enables these regeneration processes tobe efficiently executed while minimizing consumption of reductive gas,by executing the normal regeneration operation in a case of onlyperforming the DPF regeneration process being necessary, and executingthe simultaneous regeneration operation in a case in which performingthe DPF regeneration process and the SOx regeneration processsimultaneously is preferable.

Moreover, according to the present embodiment, the temperature of theexhaust is controlled by adjusting the intake air amount when executingthe normal regeneration operation. This enables the temperature of theexhaust to be controlled to a required temperature in order for the PMto be made to combust, and the DPF regeneration process to be performedefficiently.

Furthermore, according to the present embodiment, when providing thecatalytic converter 31 having an oxidative function on an upstream sideof the DPF 32, post injection is executed when executing the normalregeneration operation. With this, the temperature of the exhaustflowing into the DPF 32 can be raised and thus the DPF regenerationprocess can be performed with high efficiency, by causing fuel suppliedby way of post injection to combust by way of the catalytic converter 31when executing the normal regeneration operation.

In addition, according to the present embodiment, in a case of the PMdeposition amount QPM having become at least the first threshold valueQPMATH, the normal regeneration execution request flag FDPFRP is set to1, and the normal regeneration operation or simultaneous regenerationoperation is executed. This enables the DPF regeneration process to beexecuted at a suitable opportunity prior to the PM deposition amountreaching the limit.

Moreover, according to the present embodiment, the simultaneousregeneration execution request flag FSIMRP is set to 1, and thesimultaneous regeneration operation is executed in response to thetemperature TLNC of the NOx purification catalyst 33 being at least thepredetermined temperature judgment value TLNCTH and the SOx poisoningamount QSO of the NOx purification catalyst 33 having become at leastthe first threshold value QSOATH. This enables the SOx regenerationprocess to be performed at an opportunity before the NOx purificationperformance of the NOx purification catalyst 33 declines drastically.Furthermore, SOx desorbed from the NOx purification catalyst 33 can bepurified with good efficiency by executing the simultaneous regenerationoperation in a case in which the temperature TLNC of the NOxpurification catalyst is at least the predetermined temperature judgmentvalue TLNCTH.

In addition, according to the present embodiment, the simultaneousregeneration end request flag FSIMRE is set to 1 in response to the SOxpoisoning amount QSO having become less than the predetermined secondthreshold value SQOBTH, then execution of the simultaneous regenerationoperation ends, and the normal regeneration operation is executed. Thisenables execution of the simultaneous regeneration operation to endaccording to recovery of the NOx purification performance of the NOxpurification catalyst, and the DPF regeneration process to continue.

Moreover, according to the present embodiment, the supply amount ofreductive gas is controlled according to the exhaust air/fuel ratio AFBin a vicinity of the NOx purification catalyst 33. This enables theexhaust air/fuel ratio of exhaust flowing into the NOx purificationcatalyst 33 to be adjusted appropriately, and thus the efficiency of theSOx regeneration process to be further improved.

Furthermore, according to the present embodiment, the fuel reformer 50Bcan be made a smaller size by producing reductive gas by way of apartial oxidation reaction. In order words, this is because a device tosupply extra energy from outside does not need to be provided since thepartial oxidation reaction as described above is an exothermic reaction,and once the reaction starts, the reaction progresses spontaneously. Inaddition, there is also no need to also provide a converter and systemfor concentrating hydrogen of a shift reaction, etc. Moreover, thelight-off time of the fuel reformer 50B can be shortened by making thefuel reformer 50B to be small in this way. Therefore, reductive gas canbe quickly supplied into the exhaust plumbing 4 as needed.

Furthermore, by introducing light hydrocarbons generated secondarily inthis partial oxidation reaction to the NOx purification catalyst 33along with carbon monoxide and hydrogen, it can also be used in thepurification of SOx.

In the present embodiment, the ECU 40B configures the regenerationmeans, exhaust temperature control means, deposition amount estimationmeans, a portion of the SOx poisoning amount estimation means, a portionof the catalyst temperature estimation means, and the supply amountcontrol means. More specifically, the means related to Steps S31 to S39of FIG. 7 correspond to the regeneration means, the means related toStep S32 correspond to the exhaust temperature control means, the ECU40B and the differential pressure sensor 27 correspond to the depositionamount estimation means, the ECU 40B and the NOx sensor 28 correspond tothe SOx poisoning amount estimation means, the ECU 40B and the exhausttemperature sensor 26B correspond to the catalyst temperature estimationmeans, and the means related to Step S35 of FIG. 7 correspond to thesupply amount control means.

It should be noted that, in the aforementioned embodiment, variousmodifications thereto are possible.

For example, in the above-mentioned embodiment, although the catalyticconverter 31 having an oxidative function of continuously oxidizingreductive gas was provided in the exhaust plumbing 4 on an upstream sideof the DPF 32, it is not limited thereto. For example, a catalyst havinga similar oxidative function may be supported on the DPF, withoutproviding a catalytic converter separately from the DPF. In addition toeffects similar to the above-mentioned embodiment, this enables theexhaust emission control device to be made compact, and can promote thecombustion reaction of PM. Therefore, the efficiency of the DPFregeneration process can be further improved.

In addition, in the above-mentioned embodiment, although the intake airamount was adjusted in Step S32 of FIG. 7, it is not limited thereto,and the boost pressure may be adjusted, for example. This enableseffects similar to the above-mentioned embodiment to be exerted.

It should be noted that the present invention is not to be limited tothe aforementioned first to third embodiments, and various modificationsthereto are possible.

For example, in the above-mentioned first to third embodiments, althoughan example is shown in which the present invention is applied to adiesel internal combustion engine, the present invention can also beapplied to a gasoline internal combustion engine. In addition, thepresent invention can be applied to an exhaust emission control deviceof an engine for nautical propulsion such as an outboard engine in whichthe crank shaft is arranged vertically, or the like.

1. An exhaust emission control device for an internal combustion engineincluding a particulate filter that is provided in an exhaust channel ofthe internal combustion engine, and collects particulates in exhaust,the device comprising: a fuel reformer that is provided separately fromthe exhaust channel, produces a reducing gas containing hydrogen andcarbon monoxide by reforming fuel, and supplies the reducing gas from aninlet provided in the exhaust channel upstream of the particulate filterinto the exhaust channel; a catalytic converter that is provided in theexhaust channel between the inlet and the particulate filter, andcontinuously oxidizes the reducing gas; and a regeneration means forexecuting a regeneration process to cause particulates collected in theparticulate filter to be combusted while supplying reducing gas from thefuel reformer into the exhaust channel.
 2. An exhaust emission controldevice for an internal combustion engine including a particulate filterthat is provided in an exhaust channel of the internal combustionengine, and collects particulates in exhaust, the device comprising: afuel reformer that is provided separately from the exhaust channel,produces a reducing gas containing hydrogen and carbon monoxide byreforming fuel, and supplies the reducing gas from an inlet provided inthe exhaust channel upstream of the particulate filter into the exhaustchannel; and a regeneration means for executing a regeneration processto cause particulates collected in the particulate filter to becombusted while supplying reducing gas from the fuel reformer into theexhaust channel, wherein a catalyst having an oxidative function ofcontinuously oxidizing reducing gas is supported on the particulatefilter.
 3. An exhaust emission control device for an internal combustionengine according to claim 1, wherein the catalytic converter contains atleast one selected from the group consisting of platinum, palladium, andrhodium.
 4. An exhaust emission control device for an internalcombustion engine according to claim 2, wherein the catalyst having theoxidative function contains at least one selected from the groupconsisting of palladium, rhodium, platinum, silver, and gold.
 5. Anexhaust emission control device for an internal combustion engineaccording to claim 3, further comprising an oxygen concentrationdetection means for detecting or estimating an oxygen concentration ofexhaust in the exhaust channel flowing into the particulate filter. 6.An exhaust emission control device for an internal combustion engineaccording to claim 5, wherein the reducing gas produced by the fuelreformer contains more carbon monoxide than hydrogen.
 7. An exhaustemission control device for an internal combustion engine according toclaim 6, wherein a temperature of the reducing gas supplied by the fuelreformer is higher than a temperature of exhaust flowing through theexhaust channel at the inlet.
 8. An exhaust emission control device foran internal combustion engine according to claim 1, further comprising:a target concentration setting means for setting an oxygen concentrationtarget value of exhaust flowing into the particulate filter whileexecuting the regeneration process by way of the regeneration means; andan oxygen concentration control means for controlling the oxygenconcentration of exhaust so as to match the oxygen concentration targetvalue thus set by the oxygen concentration setting means, by adjustingat least one amount an intake air amount of the internal combustionengine, an exhaust recirculation ratio of the internal combustionengine, a fuel injection amount of the internal combustion engine, and asupply amount of reducing gas from the fuel reformer.
 9. An exhaustemission control device for an internal combustion engine according toclaim 8, wherein the target concentration setting means sets the oxygenconcentration target value based on at least one among a flow rate ofexhaust flowing through the exhaust channel, a temperature of theexhaust, and a deposition amount of particulates deposited on theparticulate filter.
 10. An exhaust emission control device for aninternal combustion engine according to claim 9, wherein the targetconcentration setting means, in a case of the internal combustion enginebeing in an idle operating state, sets the oxygen concentration targetvalue to be low compared to a case of not being in an idle operatingstate.
 11. An exhaust emission control device for an internal combustionengine according to claim 10, wherein the target concentration settingmeans, in a case of the internal combustion engine being in adeceleration operating state, sets the oxygen concentration target valueto be low compared to a case of not being in a deceleration operatingstate.
 12. An exhaust emission control device for an internal combustionengine according to claim 11, wherein the fuel reformer producesreducing gas with carbon monoxide as a main component by way of apartial oxidation reaction of hydrocarbon fuel and air.
 13. An exhaustemission control device for an internal combustion engine including aparticulate filter that is provided in an exhaust channel of theinternal combustion engine, and collects particulates in exhaust, thedevice comprising: a regeneration means for executing a regenerationprocess to cause particulates collected in the particulate filter to becombusted; and a fuel reformer that is provided separately from theexhaust channel, produces a reducing gas containing hydrogen and carbonmonoxide by reforming fuel, and supplies the reducing gas from an inletprovided in the exhaust channel upstream of the particulate filter intothe exhaust channel, wherein the regeneration means includes a normalregeneration means that executes a regeneration process withoutemploying reducing gas produced by the fuel reformer, and a heatedregeneration means that allows a regeneration process employing reducinggas produced by the fuel reformer to be executed, and switches betweenexecuting the regeneration process by way of the normal regenerationmeans and executing the regeneration process by way of the heatedregeneration means according to a predetermined condition.
 14. Anexhaust emission control device for an internal combustion engineaccording to claim 13, wherein the reducing gas produced by the fuelreformer contains more carbon monoxide than hydrogen.
 15. An exhaustemission control device for an internal combustion engine according toclaim 13, wherein the catalytic converter that continuously oxidizesreducing gas is provided in the exhaust channel between the inlet andthe particulate filter.
 16. An exhaust emission control device for aninternal combustion engine according to claim 13, further comprising acombustion judgment means for judging whether particulates deposited onthe particulate filter are in a combusted state, wherein theregeneration means executes the regeneration process by way of thenormal regeneration means in a case of having been judged that theparticulate are in a combusted state, and executes the regenerationprocess by way of the heated regeneration means in a case of having beenjudged that the particulates are not in a combusted state.
 17. Anexhaust emission control device for an internal combustion engineaccording to claim 16, further comprising an oxygen concentrationdetection means for detecting or estimating an oxygen concentration ofexhaust in the exhaust channel on a downstream side of the particulatefilter, wherein the combustion judgment means judges whether theparticulates are in a combusted state based on the oxygen concentrationthus detected or estimated by the oxygen concentration detection means.18. An exhaust emission control device for an internal combustion engineaccording to claim 16, further comprising a downstream exhausttemperature detection means for detecting or estimating an exhausttemperature in the exhaust channel on a downstream side of theparticulate filter, wherein the combustion judgment means judges whetherthe particulates are in a combusted state based on the exhausttemperature thus detected or estimated by the downstream exhausttemperature detection means.
 19. An exhaust emission control device foran internal combustion engine according to claim 16, wherein the heatedregeneration means reduces the intake air amount of the internalcombustion engine, increases the exhaust recirculation ratio of theinternal combustion engine, or sets the charge efficiency of theinternal combustion engine to be small, compared to a case of performingthe regeneration process by way of the normal regeneration means.
 20. Anexhaust emission control device for an internal combustion engineaccording to claim 19, wherein the heated regeneration means includes afirst heated regeneration means for executing a regeneration processwhile supplying reducing gas from the fuel reformer into the exhaustchannel, and a second heated regeneration means for executing aregeneration process without supplying reducing gas from the fuelreformer into the exhaust channel, and switches between executing theregeneration process by way of the first heated regeneration means andexecuting the regeneration process by way of the second heatedregeneration means according to a predetermined condition.
 21. Anexhaust emission control device for an internal combustion engineaccording to claim 20, further comprising an upstream exhausttemperature detection means for detecting or estimating a temperature ofexhaust in the exhaust channel on an upstream side of the particulatefilter, wherein the heated regeneration means executes the regenerationprocess by way of the first heated regeneration means in a case of thetemperature thus detected by the upstream exhaust temperature detectionmeans being lower than a predetermined judgment value.
 22. An exhaustemission control device for an internal combustion engine according toclaim 20, further comprising a filter temperature estimation means forestimating or detecting a temperature of the particulate filter, whereinthe heated regeneration means executes the regeneration process by wayof the first heated regeneration means in a case of the temperature thusestimated or detected by the filter temperature estimation means beinglower than a predetermined judgment value.
 23. An exhaust emissioncontrol device for an internal combustion engine according to claim 20,further comprising a torque estimation means for estimating a generatedtorque of the internal combustion engine, wherein the heatedregeneration means executes the regeneration process by way of the firstregeneration means in a case of the generated torque thus estimated ordetected by the torque estimation means being less than a predeterminedjudgment value.
 24. An exhaust emission control device for an internalcombustion engine according to claim 23, wherein the torque estimationmeans estimates the generated torque of the internal combustion enginebased on at least one among a revolution speed of the internalcombustion engine, a fuel injection amount, and a fuel injection timing.25. An exhaust emission control device for an internal combustion engineaccording to claim 20 further comprising a timing means for measuring anelapsed time since starting up the internal combustion engine, whereinthe heated regeneration means executes the regeneration process by wayof the first heated regeneration means in a case of the elapsed timethus measured by the timing means being less than a predeterminedjudgment value.
 26. An exhaust emission control device for an internalcombustion engine, including a NOx purification catalyst that isprovided in an exhaust channel of the internal combustion engine andthat, with an air/fuel ratio of exhaust flowing through the exhaustchannel as an exhaust air/fuel ratio, adsorbs or occludes NOx in exhaustwhen the exhaust air/fuel ratio is made lean, and reduces the NOxadsorbed or occluded when the exhaust air fuel ratio is made rich, and aparticulate filter that is provided in the exhaust channel furtherupstream than the NOx purification catalyst, and that collectsparticulates in exhaust, the device comprising: a fuel reformer that isprovided separately from the exhaust channel, produces a reducing gascontaining hydrogen and carbon monoxide by reforming fuel, and suppliesthe reducing gas from an inlet provided in the exhaust channel betweenthe particulate filter and the NOx purification catalyst into theexhaust channel.
 27. An exhaust emission control device for an internalcombustion engine according to claim 26, wherein the reducing gasproduced by the fuel reformer is at a pressure higher than atmosphericpressure, and contains more carbon monoxide than hydrogen by volumeratio.
 28. An exhaust emission control device for an internal combustionengine according to claim 26, wherein a temperature of the reducing gassupplied by the fuel reformer is higher than a temperature of exhaustflowing through the exhaust channel at the inlet.
 29. An exhaustemission control device for an internal combustion engine according toclaim 26, wherein oxygen is contained in the exhaust flowing through theexhaust channel when reducing gas from the fuel reformer is introducedinto the exhaust channel.
 30. An exhaust emission control device for aninternal combustion engine according to claim 26 further comprising: aregeneration means for selectively executing a normal regenerationoperation that raises the particulate filter in temperature to causeparticulates collected in the particulate filter to combust, and asimultaneous regeneration operation that supplies reducing gas from thefuel reformer into the exhaust channel while executing the normalregeneration operation to purify SOx adsorbed to the NOx purificationcatalyst according to a predetermined condition.
 31. An exhaust emissioncontrol device for an internal combustion engine according to claim 30,further comprising an exhaust temperature control means for controllinga temperature of exhaust when executing the normal regenerationoperation by adjusting at least one among an intake air amount and boostpressure.
 32. An exhaust emission control device for an internalcombustion engine according to claim 30, wherein a catalytic converterhaving an oxidative function is provided in the exhaust channel on anupstream side of the particulate filter, and wherein the regenerationmeans executes post injection when executing the normal regenerationoperation.
 33. An exhaust emission control device for an internalcombustion engine according to claim 30, wherein a catalyst having anoxidative function is supported on the particulate filter, and whereinthe regeneration means executes post injection when executing the normalregeneration operation.
 34. An exhaust emission control device for aninternal combustion engine according to claim 30, further comprising aparticulate deposition amount estimation means for estimating ordetecting a particulate deposition amount of the particulate filter,wherein the regeneration means executes the normal regenerationoperation or the simultaneous regeneration operation in response to theparticulate deposition amount thus estimated or detected by theparticulate deposition amount estimation means having become at least apredetermined first estimation judgment value.
 35. An exhaust emissioncontrol device for an internal combustion engine according to claim 30,further comprising: a catalyst temperature estimation means forestimating or detecting a temperature of the NOx purification catalyst;and a SOx poisoning amount estimation means for estimating or detectinga SOx poisoning amount of the NOx purification catalyst, wherein theregeneration means executes the simultaneous regeneration operation inresponse to the temperature thus estimated or detected by the catalysttemperature estimation means being at least a predetermined temperaturejudgment value, and the SOx poisoning amount thus estimated or detectedby the SOx poisoning amount estimation means having become at least apredetermined first poisoning judgment value.
 36. An exhaust emissioncontrol device for an internal combustion engine according to claim 35,wherein the regeneration means ends execution of the simultaneousregeneration operation and executes the normal regeneration operation,in response to the SOx poisoning amount estimated or detected by the SOxpoisoning amount estimation means having become smaller than apredetermined second poisoning judgment value.
 37. An exhaust emissioncontrol device for an internal combustion engine according to claim 26,further comprising: an oxygen concentration detection means fordetecting an oxygen concentration of exhaust in the exhaust channel in avicinity of the NOx purification catalyst; and a supply amount controlmeans for controlling a supply amount of reducing gas supplied from thefuel reformer into the exhaust channel, according to the oxygenconcentration thus detected by the oxygen concentration detection means.38. An exhaust emission control device for an internal combustion engineaccording to claim 26, wherein the fuel reformer produces reducing gasby way of a partial oxidation reaction of hydrocarbon fuel and air. 39.An exhaust emission control device for an internal combustion engineaccording to claim 26, wherein the internal combustion engine uses lightoil as fuel, and combusts the fuel by way of compression ignition.